SHANKAR VEDANTAM, HOST: Shankar here. I know what you're thinking. It's not Monday night. Why is there a new HIDDEN BRAIN in my feed? Well, I want to fill you in on an exciting development. A few weeks ago, HIDDEN BRAIN made its debut on more than 130 public radio stations around the United States, from Washington, D.C., to Wailea, Hawaii. That's right - along with being a podcast, we're now a radio show.UNIDENTIFIED CHILDREN: Yay.VEDANTAM: What you're about to hear is our radio program from last week. It ties together two of our favorite podcast episodes - What Are The Odds and The Ikea Effect. The next 50 minutes are about narcissism and some of the clever ways it manifests in our daily lives. I think you'll really enjoy it. We'll be posting radio replays a couple of times a month. Some of them will be combinations of earlier podcast episodes, while others are going to bring in new material. Look for the shows in your feed on Friday evenings. OK. Here's today's show.(SOUNDBITE OF MUSIC)VEDANTAM: This is HIDDEN BRAIN. I'm Shankar Vedantam. Have you ever had the experience of going to a party or office get-together and meeting someone with the same name, the same birthday? Maybe you've gone on vacation to some far-flung locale and met someone who lives down the street from you. Many of us are drawn to coincidences like this. They make us wonder, how in the world did that happen? What does it mean?Today, we explore our deep fascination with these moments of serendipity. New research suggests they reveal important things about how our minds work, and they have a far more powerful effect on our lives than any of us imagine. A couple of months ago, we asked HIDDEN BRAIN listeners to share coincidences that they'd experienced. Lots of people called in with amazing stories. Within those stories, we found two that themselves formed a coincidence.AMANDA BIRCH: So I was a student at the University of Rhode Island, and we were in this writing class.VEDANTAM: This is Amanda Birch (ph). She was talking to the teacher of her writing class, and the teacher mentioned that she lived in a small town in Vermont. The same small town, it turned out, where Amanda's mother had grown up. The teacher asked Amanda what her mother's maiden name was and Amanda told her.BIRCH: And she just kind of drops her pen. And she goes, you're not going to believe this, but I live in the house where your mother grew up.VEDANTAM: The other listener who called us was Sarah Toperav (ph). She called us on a scratchy phone line from Paris. Sarah's an American but has been living in France for several years. She was at a house party, and someone there told her that there was another American in the room. So she went over to say hello. They started talking, and...SARAH TOPERAV: So it turns out that this girl that I met at this house party in Paris grew up in the exact same house in Poughkeepsie, N.Y., as my father.(SOUNDBITE OF MUSIC)VEDANTAM: What are the odds? We thought we might find out. On today's show, we'll talk about the mathematics of coincidences and why we find them so intriguing. We'll start today with a story about Whisper, which is an app that allows users to connect anonymously online. People can post their secrets on the site, and strangers can respond with their own whispers. The messages are short, about the length of a tweet, and they range from the silly...UNIDENTIFIED MAN #1: (Whispering) As a teacher, I'm not supposed to have favorite students but I definitely do.UNIDENTIFIED MAN #2: (Whispering) I just want someone to look at me the way I look at tacos.VEDANTAM: ...To the very serious.UNIDENTIFIED WOMAN #1: (Whispering) I'm having an abortion on Monday.UNIDENTIFIED WOMAN #2: (Whispering) My husband cheated on me. Should I forgive him?VEDANTAM: Some months ago, the folks at Whisper got in touch to tell us a story about an interesting coincidence that happened on their site. Lauren Hudson (ph) is 27, and she turned to Whisper at one of the darkest moments of her life.LAUREN HUDSON: I was in a really bad relationship. There was a lot of domestic violence involved. And I didn't really know what to do or how to reach out to people or how to talk about it, so I used the app to connect with other women. And it's a kind of vent and, like, find empowerment to get away from the person that I was with.VEDANTAM: Lauren was having trouble opening up about what was happening with her friends and family.HUDSON: I think I was scared, to be completely honest. I think I had a lot of fear. And I didn't want, like, any police involved. I didn't want, like - I didn't want it to turn into, like, this whole thing.VEDANTAM: But on Whisper, she could be anonymous. She could seek support without all the immediate consequences. It was there in one of these threads that she started talking to a man. Lauren was touched by how much compassion he seemed to have for her, a complete stranger.HUDSON: It was almost as if he genuinely wanted to know how I was, even though he didn't know who I was. And he knew that it was anonymous. And who knows who he's talking to? He just genuinely wanted to know if I was OK.VEDANTAM: He was in a town nearby, another coincidence perhaps. And they started exchanging messages. They connected immediately, decided to meet in person.HUDSON: We got together, and we went to Applebee's. And we sat and we talked for like - I think it was like almost two hours that we just sat and talked.VEDANTAM: They became more and more inseparable. Lauren ended her unhealthy relationship and started dating this guy from Whisper, Eric (ph). And everything was going great, but Lauren was a little nervous about meeting Eric's family. Eric had brought Lauren home to have dinner with them. And the whole time, she was anxious.HUDSON: Like, my palms were sweating. And I felt like really hot, you know? (Laughter) So I didn't know if like - if it was going down well or if I was totally blowing it. Like, I didn't know what was going on.VEDANTAM: She was especially nervous about Eric's sister, Amanda (ph).HUDSON: You know, I knew when I first met her - the first couple times that we hung out and stuff, I knew that there was a little bit of a distance there. And I knew that every time I went over to, you know, hang out with Eric and his family, that those walls would slowly break down.VEDANTAM: Lauren understood Amanda's attitude. She felt the same toward the girls her younger brother would bring home.HUDSON: Maybe I'll see them next week, you know, or maybe I'll never see them again. You know what I mean? So that was kind of like what I had in my head. I was like, well, I hope that - you know, I'm thinking, I hope that they know that I'm not going anywhere.VEDANTAM: Lauren wasn't going anywhere. She and Eric were getting engaged. Eric, in fact, had a flair for the romantic, bringing her roses, comforting her with her favorite movie after a tough day. And he would tell his family about all this. So why couldn't Lauren break through with Amanda? All this time, Lauren was still on Whisper.HUDSON: Now I use it - instead of me looking for help, I use it to help others. That's my way of giving back because the Whisper community helped me when I needed them.VEDANTAM: One day, she started exchanging messages with a woman who was going through a very painful breakup.HUDSON: I sent a big message basically saying that it's OK, everyone goes through heartaches. And there'll be many more people out there.VEDANTAM: As a way to offer encouragement, Lauren told the woman about her own happy relationship. The woman asked Lauren about the nicest thing her fiance had done for her. Lauren told her about the day Eric surprised her with her favorite movie.HUDSON: On my birthday, I had a really bad day at work. It was like one of those days were like, you know, you wake up and just from the moment you put your feet on the floor, like, everything goes wrong. So I was just - I didn't want to see him that day. I was just miserable. I just wanted to be home. Like, I was just like - I just want to go to bed. And he surprised me with these beautiful flowers, these roses. And he had "The Notebook," which is my favorite, like, sappy love story of all time.VEDANTAM: Lauren finished telling her story and waited for a reply.HUDSON: Her first response after I sent that story to her, she's like, Lauren? (Laughter) Like, she - Lauren? I was like, how do you know my name? You know, because it's all anonymous. And she's like, this is Amanda.VEDANTAM: Amanda, Eric's sister, the very person she had been trying so desperately to connect with in real life. Lauren says this coincidence changed her whole relationship with Amanda. Connecting randomly online and revealing intimate details about themselves made the two women feel closer. Many of us have experienced these kinds of coincidences. You bump into your kindergarten friend your first day in college or you meet someone at a party and discover she lives in your dad's childhood home in Poughkeepsie.When these kinds of coincidences happen in our lives, they feel like magic. But as any mathematician will tell you, things that feel unusual or even impossible are actually fairly common. Mathematician Joseph Mazur knows this, but he was reluctant to write a book that would dispel the magic.JOSEPH MAZUR: Coincidences are wonderful stories. I don't want to blow the stories in favor of the mathematics because, you know, I was hitting a nerve on coincidences.VEDANTAM: In the end, though, Joseph did write his book. It's called "Fluke: The Math And Myth Of Coincidence." It's full of stories of people who find themselves experiencing things that feel so unlikely. But Joseph Mazur says if you study this for a while, the coincidences start to fall into certain categories. And the stories we heard from our two listeners, as well as Lauren's story about meeting her soon-to-be sister-in-law on Whisper, are all basically the same type of coincidence, which in itself is not a coincidence.MAZUR: If you categorize these coincidences to, let's say, 10 different categories, that particular kind of coincidence - meeting an acquaintance or somebody you're familiar with in a very strange place - I would say perhaps 80 percent of all the coincidences I've heard fall into that category.VEDANTAM: Joseph Mazur says the reason these coincidences feel extraordinary but actually are not so extraordinary is because of a common misconception about the number of people we think we actually know.MAZUR: People think that their address book is essentially the peoples they know. And it turns that any particular address book is about 1 percent of the peoples they actually know in some way. In other words, a neighbor, somebody they bump into in the street. But the address book is about 1 percent of the people they know.VEDANTAM: As a result, the odds of bumping into someone you know are much greater than you think because you know many more people than you think.(SOUNDBITE OF MUSIC)VEDANTAM: Sometimes math can help us understand the magic, magic like winning the lottery not just once but several times. That's what happened to a woman named Joan Ginther.MAZUR: In 1993, I think it was, she won $5.4 million in Texas lotto. Thirteen years later, she won again - $2 million. And then a few years after that, she won $3 million. And then in 2010, she won $10 million.VEDANTAM: What are the odds of one person winning the lottery four times?MAZUR: Yeah. The odds are - I think somebody made a calculation, and I did too, that the odds are about 18 septillion to one against it happening.(SOUNDBITE OF MUSIC)VEDANTAM: Eighteen septillion to one - that's incomprehensible. For those who are not mathematicians, a septillion is one followed by 24 zeroes. But Joseph Mazur says we're actually asking the wrong question. Think about it this way. If I buy a lottery ticket and I ask the question, what are the odds that I will win, my odds are very small.But if I ask, what are the odds that anyone will win the lottery, in a country of hundreds of millions of people, the odds are actually much higher. So if you ask the question slightly differently, not what are the odds that Joan Ginther will win the lottery four times, but what are the odds that anyone will win four times? You get a very different answer.MAZUR: I think I calculated at one point about 5 million to 1, which is not anywhere near the septillions. It's about 5 million to 1. And that - it takes into account the fact that we have thousands of lotteries in the world. I mean, there are many lotteries, and many of them are big-time lotteries.VEDANTAM: So 5 million to 1 - still unlikely but not incomprehensible. What makes it even more comprehensible is the fact that most lottery winners don't stop gambling when they win.MAZUR: And you do find that almost everybody who does win a lottery fairly big-time spends all that money or much of that money in trying to win again.VEDANTAM: Joseph Mazur says this might have been the case with Joan Ginther.MAZUR: You win $5.4 million. You have money to play with. You have house money. So you're taking the house money to bet again. And her odds of winning a second time are better than most people's because she's got the money to play with. She wins a second time. Then she's playing with more money. And you can see the - between the first winning and the second winning, it was 13 years. Between the second winning and the third, it was only two years. And between the third and the fourth, it was only two years as well.VEDANTAM: So Joseph Mazur can wrap his head around what happened to Joan Ginther, but there are some coincidences that just defy mathematical interpretation. Joseph told me one of his favorite stories about a 19th century French poet, Emile Deschamps.(SOUNDBITE OF ACCORDIAN MUSIC)MAZUR: Emile Deschamps - as a teenager, he meets a man by the name of - a strange name - Monsieur de Fontgibu (ph).(SOUNDBITE OF ACCORDIAN MUSIC)MAZUR: He turns out to be an immigrant from England. And Fontgibu introduces him to a plum pudding. It's a very English dish, and it's almost unheard of in France.VEDANTAM: Ten years go by, and Deschamps is passing a restaurant in Paris. There's a sign on the window saying that they have plum pudding on their menu. But when Deschamps goes inside, he's told the last of the plum pudding was just sold to a gentleman sitting in the back.MAZUR: And the waiter calls out loud, Monsieur de Fontgibu, would you be willing to share your plum pudding with this gentleman?VEDANTAM: Years pass. Deschamps is now at a dinner party with some friends. The host announces an unusual dessert will be served - plum pudding.MAZUR: (Laughter) And Deschamps jokes that one of the guests to arrive must be Monsieur de Fontgibu. Well, soon the doorbell rings, and Monsieur de Fontgibu is announced. And he enters. He's an old man by now, but Deschamps recognizes him. Monsieur de Fontgibu looks around and realizes that he's in the wrong apartment. He was invited to a dinner but not in that apartment.(SOUNDBITE OF ACCORDIAN MUSIC)MAZUR: I love that because it's - you know, it's a triple coincidence. And it has a beautiful story element with it. I mean, that's so magnificent. And that's why - that's the kind of coincidence I love to hear.VEDANTAM: Joseph Mazur, professor of mathematics and author of "Fluke: The Math And Myth Of Coincidence." When we come back, we're going to look at what coincidences reveal about the mind. In particular, I'm fascinated by something I've observed in my own life. When I experience a coincidence, it invariably feels more meaningful to me than it does to others. This is HIDDEN BRAIN. I'm Shankar Vedantam. Stay with us.(SOUNDBITE OF MUSIC)VEDANTAM: Welcome back to HIDDEN BRAIN. I'm Shankar Vedantam. I'm fascinated by coincidences and could listen for hours to stories about them. But what is it that so fascinates us about these moments in life? At the University of Chicago, psychologist Nick Epley thinks he might have one answer. He's the author of the book "Mindwise." To understand how Epley thinks about coincidences, I need to take a moment and explain his broader work to you first.Epley's book examines how we read the mental states and intentions of other people. This is a remarkably useful skill, but we sometimes misapply it. We sometimes attribute intentionality to things that aren't even living, especially when they're out of the ordinary. For example, we don't personify a sunny day, but we give hurricanes a name - Katrina, Sandy, Andrew.After Hurricane Katrina, the mayor of New Orleans said, God must be mad at America. This isn't new. For centuries, people have ascribed intentionality to natural forces. We think storms, droughts and earthquakes must have a mind of their own.NICK EPLEY: This general tendency to explain behaviors in terms of purpose or intent or meaning is often quite a successful thing to do. Turns out we live with other people who do have intentions and goals and foresight and planning and meaning behind their actions. And so by and large, that tendency to make those kinds of attributions to other people is a good way to learn about each other, is a good way to explain why other people did something in the past, to predict how they're likely to behave in the future.But the problem with any kind of good tool is that sometimes we use it a little too much. And that's what happens in these cases where you're trying to explain the behavior of something that doesn't really have a sensible explanation for it - some random event, some chance occurrence, some physical anomaly, some weather pattern that crops up that might not in fact have a mind behind it.VEDANTAM: This is why we are fascinated by robots that move in unpredictable ways.EPLEY: What we found was that when people were given a description of an object that made it sound unpredictable, like you couldn't anticipate its actions, that's when people described it or reported that it had more mental states. They were more willing to say that the object has a mind of its own - that it has intentions, for instance. And I don't think this is totally counterintuitive.That is, a mind - if you see, for instance, a billiard ball sitting on a table - another ball comes along and hits it and that ball rolls off in the predicted direction. Well, you don't need anything to explain that. But if you've got a ball sitting on a table, and it suddenly starts rolling around randomly - well, then you've got something to explain.And in these cases, sometimes people look to the inside of an agent - give it a mind. Maybe the ball is possessed. Maybe there is a demon controlling it, moving it around the table. Sometimes people attribute a mind to something when it's not there. But they do that as an effort to explain what's going on in this autonomous agent. And they're more likely to do that when an agent behaves somewhat unpredictably.VEDANTAM: I was over at a friend's house. And my friend has a wonderful pool. And he had set the - this underwater Roomba, for the lack of a better term, to clean the bottom of the pool. So it sort of rolls around the bottom of the pool. And it goes in this completely random fashion, right?So it just runs for a couple of hours. It's cleaning the bottom of the pool. And I found myself fascinated just watching it because the fact that you can't predict what it's going to do next makes it just more interesting and more alive in a way than something that moves in a very predictable fashion.EPLEY: Absolutely. Something that moves robotically, very predictably - that is just a mindless machine. But when your Roomba is going around randomly, well, now it wants to go over there a little bit. Now it wants to move over here. Now it realizes it didn't clean that side of the pool over there. Things that behave randomly start to get a little sense of a mind.Now, people aren't crazy. You don't think it's like your mother - right? - or your - you know, your spouse who's vacuuming the living room. But it starts to look just a little bit more mindful. In fact, a Roomba is a good example. People actually do name their Roombas. You can buy outfits to dress it up. If you Google this online, you'll find all kinds of examples of people thinking of their Roombas as having, perhaps, a little bit more of a mind than it really does.VEDANTAM: I want to talk to you a little bit about the subject of coincidences. And I thought of you and your work because it feels to me that when something unusual happens to us and we stop, and we say, that is weird; I was just reading this word in a book a second ago, and someone in the room around me mentions the very same word. And it makes you stop and look up, just like I stop and look at that underwater Roomba.EPLEY: Absolutely. That's a case where something unusual happens. It was unpredictable. And you tried to explain it. You can explain these kinds of random coincidences in lots of different ways. There are lots of different kinds of causal structures we might be able to put on it. But some of them involve giving it more meaning than it actually has.(SOUNDBITE OF MUSIC)VEDANTAM: This is what underwater Roombas have to do with coincidences. Like a robot that does something unexpected, coincidences cry out for meaning or explanation because they're out of the ordinary. We start to see patterns even when there aren't any.EPLEY: My favorite example of this in the world of psychology is actually a phenomena first documented by my Ph.D. adviser Tom Gilovich and the brilliant psychologist Amos Tversky. It was the illusion of the hot hand in basketball.(SOUNDBITE OF ARCHIVED RECORDING)UNIDENTIFIED ANNOUNCER: Danny Green again from downtown. He's hit six in a row going back to Game 2.VEDANTAM: The myth is that basketball players get on a roll.EPLEY: People believe that basketball players get a hot hand and that there are times when they're on, and the chance of making a basket is higher after they've just made one then after they've just missed one.VEDANTAM: Epley isn't saying basketball players don't have streaks. He's saying we draw the wrong conclusions about these streaks.EPLEY: Let's imagine that they're a good shooter, and they shoot 50 percent from the field. That 50 percent probability is going to produce a lot more clumping in the baskets than people expect. People expect a coin flip - a 50 percent probability - to alternate a lot more than it actually does. And so when you see randomness out in the world, it actually looks more ordered to you than it really is.(SOUNDBITE OF ARCHIVED RECORDING)UNIDENTIFIED ANNOUNCER: Fifteen 3-pointers for the Spurs.VEDANTAM: Epley described a party trick that demonstrates this phenomenon. You can do this, too. Give everyone in the party a notecard and have them write down what they think 30 coin flips would look like - H, if they think it will be heads, T, if they think it'll be tails.EPLEY: You then, as master magician, leave the room. And you have one person come up and actually flip a coin 30 times.VEDANTAM: That person writes down the actual sequence of coin flips on a notecard and then collects all the note cards - the real and the imagined sequences - and puts them together. You, the magician, then come back into the room and identify the card that was the real coin flip.EPLEY: And the way you do this is you look for the card that has the longest runs because people's imagination doesn't presume that a 50/50 probability will produce very long runs. And so people's imagined coin flips will alternate more than the real coin flip will, and that's how you can identify the real one from the fake ones.And I think that illusion that we have that randomness alternates or is more chancy than it actually, that there's less clumping, is also the thing that gives rise to these other phenomena where we see randomness in the world and we see more predictability or intentionality than actually exists in it.VEDANTAM: When we asked our listeners to share coincidences with us, many of them wrote in with really interesting examples of things that happened to them. One thing that I was struck by is the sense that sometimes a coincidence seems more meaningful to you than it does to someone else. So, for example, when I'm reading a book and I come by an unusual word and then someone in the room mentions that same word, to me, it feels like it's a sign of something.But if I were to tell you - I say, Nick, you know, this happened to me yesterday, you'd say, yeah, sure; that's going to happen once every month or so. It's exactly what you would expect if you believe the laws of probability. Why do you think it is that coincidences are more meaningful to us than to other people?EPLEY: That's a really good question. I actually don't know that I've seen any research that demonstrates that phenomena. But that strikes me as a very compelling hypothesis. I think that's probably likely to be right. And I think the reason why coincidences seem very meaningful in the first place is that you're trying to explain them.You and I both thought of the word propeller at the same time. How on earth could that be that Shankar was thinking about propeller at the same time that I was? And so you're trying to explain that. You're focusing on that event that just happened to you. It has personal relevance to you.That makes it impactful, but it also makes you somewhat myopic. And what we don't think about are all of the other things that any of us in the room could have thought about at the same time that might also have seemed amazing to us. We're trying to explain this one thing because it's so meaningful to us. It just happened to us. Other people are less likely to be that myopic, I think, and so they would be likely to think about other things that could have happened to you, which would make it seem less amazing to them.VEDANTAM: We, of course, experienced this ourselves here on the show when two listeners called in with eerily similar coincidence stories. I described these two stories to Nick about women who ran into people who turned out to live in the very same house where the women's parents had grown up.So these are not just two coincidences. These are two coincidences that both happened to us at HIDDEN BRAIN, which seems truly extraordinary, Nick.EPLEY: (Laughter) How could that possibly be that you get these two that are exactly the same? It's magic, is what it is, Shankar. You're magical.VEDANTAM: That's really just all I wanted to hear you say, Nick. It's been 20 minutes to get that out of you.EPLEY: (Laughter) Eventually, we have to give in to the laws of probability. There's nothing that can explain that, right?VEDANTAM: Nick, I want to thank you for talking with us today.EPLEY: Yeah. Thanks for having me.VEDANTAM: Nick Epley - he's the author of "Mindwise: How We Understand What Others Think, Believe, Feel And Want."(SOUNDBITE OF MUSIC)VEDANTAM: Not long after I finished talking to Nick Epley, I came by some new work that made me think about coincidences very differently. Yes, coincidences can feel magical. And they do reveal important things about how our minds work. But there's also psychological research that shows coincidences can actually change the direction of our lives. They can be powerfully meaningful.UNIDENTIFIED MAN #3: The girl that I'm dating now - we have the same birthday, which is kind of cool.UNIDENTIFIED WOMAN #3: My fiance, Israel (ph), and I have the same birthday, which is something we discovered on our second date.VEDANTAM: At first, these may seem like garden-variety coincidences. Two people start dating. They discover they have the same birthday. But there's evidence this may be more than just a kind of coincidence we've been talking about so far on the show. Having a common birthday seems to actually draw people closer to one another.UNIDENTIFIED WOMAN #2: When I first went to a new hairstylist, we found out that we had the same birthday, and we called each other birthday twins. And I wound up going to that hairstylist for years, even after she switched salons, even after we moved. I would drive 40 minutes to go get my haircut by her.VEDANTAM: Some people see so much significance in shared birthdays or even shared numbers in two birthdays that they select dates for important events based on those patterns.JEANETTA CRAVENS: My birthday is October 27. And with my first husband, his birthday was September 27. And we had the opportunity to get married on August 27. It was a no-brainer. We decided to do that.VEDANTAM: The woman you just heard, Jeanetta Cravens (ph) from Oklahoma City, says her love for people with the same birthday extends beyond her love life.CRAVENS: October 27 is also Teddy Roosevelt's birthday, and so I've always felt a little affinity for him and for his leadership.VEDANTAM: Shared birthdays, in fact, aren't the only thing that draw people closer to one another. Jeanetta also finds herself drawn to people who happen to have the same name.CRAVENS: When I meet another Jeanetta, there is an automatic, like, oh, my gosh. I can't believe we have the same name. And then it happens to be that we have the same spelling. And I'll tell you, I've only met two people who have the same spelling as me. But I can tell you who they are. And I felt an automatic kinship.(SOUNDBITE OF MUSIC)VEDANTAM: This is not just Jeanetta. All of us are affected by what researchers call implicit egotism.BRETT PELHAM: Carpenters working in carpentry. Bakers working as bakers. Butchers working as butchers.VEDANTAM: Stay with us.(SOUNDBITE OF MUSIC)VEDANTAM: This is HIDDEN BRAIN. I'm Shankar Vedantam. In Greek mythology, the hunter, Narcissus, was so enamored by his own beauty that he fell in love with a reflection of himself. Modern psychology shows that we all have a little bit of Narcissus in us. Most of us like people who remind us of ourselves, whether that's someone with the same name or someone with the same birthday.Most of the time, such self-love is amusing and harmless, maybe even beneficial - a sign of good self-esteem. But there are times when falling in love with ourselves or with people who remind us of ourselves can be a real problem.Brett Pelham is a professor of psychology at Montgomery College in Maryland. He studies something called implicit egotism...PELHAM: Which is the idea that many biases are unconscious. And one very well-studied bias was egotism - valuing the self favorably, protecting the self and so forth. And so we simply got the idea that there's several different things that, at least to some degree, reflect a preference for the self and attraction to things that resemble the self.VEDANTAM: ...Like having an affinity for someone with the same birthday or someone with the same name or even going into a profession that sounds like an echo of your name.PELHAM: So we originally looked at whether people named Dennis or Denise gravitate toward dentistry.VEDANTAM: (Laughter).PELHAM: But we learned pretty quickly that it's really hard to get data on those things. So you know, you - there aren't great directories of medical professionals. There is a guy named Abel (ph) who was able to document - and I was a review on his paper, and I was...VEDANTAM: So now every time you say this, I'm going to jump in and say, a guy named Abel who was able to do something.PELHAM: He was able to do a lot of things. He showed that people whose last name is Doctor or whose last name is the word lawyer - the name Lawyer - gravitated toward those two professions.VEDANTAM: There are lots of other examples. Brett looked at a massive database of millions of Americans' names from the recently released 1940 census to examine if there were broad patterns like...PELHAM: Carpenters working in carpentry. Bakers working as bakers. Butchers working as butchers. Miners working as miners. Masons working as masons. So we looked at every surname there is - currently the top 2,000 surnames - that happens to be a career name. And we looked at all of them. There're 11 of them that are pretty common. I just listed a few.And for every single surname in the 1940 census with something like a - I think it is was 130 million people - we were able to show that for every single surname, there was at least a weak tendency for people to gravitate toward careers that perfectly matched their last names.VEDANTAM: So the obvious thing to say, of course, is that the reason you have a slightly larger number of Carpenters be carpenters is that the name Carpenter probably originated from families who were in carpentry. And so there is some kind of ancestral connection to the profession that is driving both the names and the choices.PELHAM: Quite possibly, but if you do the math, you pretty quickly see, it gets to be a pretty tiny percentage of people. So if you assume that even over 10 generations, there's a 50 percent chance that you did what your dad did and a 50 percent chance that he did what his grandfather did, which is probably higher than reality, you're talking about a probability of less than 1 in 1,000 already over 10 generations.In other words, surnames are so old, and they change hands. You know, when woman named Carpenter marries a guy named Farmer, for example, that that's really - it really just can't account for an effect anywhere near this magnitude.(SOUNDBITE OF DOUBLE DECK'S "FORA DO NORMAL")VEDANTAM: Brett Pelham has looked at large data sets and public records like the Social Security Death Index or state marriage records - databases with information about millions of Americans. And he and his fellow researchers have seen all kinds of funny effects, like, for example, one listener called in to say she and her husband were both born on the 25th day of different months. This isn't as uncommon as you might think, beyond what you might expect by mere chance.PELHAM: And there's about a 7 percent bias in that direction. So if you should have a thousand people doing that, you have 1,070 people doing that.VEDANTAM: If that doesn't sound like a lot, you're right. You should think of implicit egotism as a tiny, invisible nudge. It won't shape what everyone does all the time, but it does shape what some people do some of the time. It's when you multiply the small effects over hundreds of millions of people that you start to see lots of examples. Brett says that if you really love your birthday, the effect gets even larger.PELHAM: Our operational definition of really loving your birthday was getting married on your birthday number. So if you got married on the 13th of the month, you were quite a bit more likely to marry another person who also had the number 13 as his birthday number.VEDANTAM: Again, Brett calls this an implicit bias for a reason. You may not be consciously choosing things as important as your spouse or your profession or the place you call home based on arbitrary factors like your name or your birthday. He thinks the bias comes about simply because we like our names and our birthdays and have positive associations with them.PELHAM: And so you just associate your name with all the wonderful things that come along with that. And the best bit of evidence I have that I've never bothered to publish is, there's one part of people's names they don't like that much, and that's their middle names. You know, the joke about that is, the sole purpose of a child's middle name is to know when he's really in trouble - and my additional comment is to know if he might be a serial killer someday, right? So the middle name is not nearly as loved as the first or the last name. People feel very ambivalent about their middle name.VEDANTAM: There can be other reasons for ambivalence. Sometimes we dislike it when another person has the same birthday. If you were born on April 20, you might hate the fact Hitler was born on that day too. Brett finds that if a consumer product happens to have your name on it but is poorly built, you are more likely to hate that product. People dislike seeing something inferior in the world that has their name on it.(SOUNDBITE OF MUSIC)VEDANTAM: As Brett and I were talking, I realized something a little uncomfortable - that I myself had fallen prey to implicit egotism.You know, as you're talking right now, I am realizing something about myself for the very first time. There is - there was a philosopher in India whose name was Shankara - my name. And he actually taught a philosophy that is known as Vedanta.PELHAM: Wow.VEDANTAM: And I've always been drawn to the fact that I find the philosophy of Vedanta to be very interesting, and the fact that Shankara taught that philosophy, I thought was just charming. But now as I'm listening to you say this, I'm realizing that this could just be implicit egotism.PELHAM: I've read his work very well, and it truly is wonderful. It's brilliant, so I think in this case, you made the objectively good decision, yeah.VEDANTAM: (Laughter) At the same time, it does make you think, though.PELHAM: Absolutely, yes.VEDANTAM: Has this ever happened to you, Brett? Do you ever think about yourself and how implicit egotism is affecting you?PELHAM: We're getting a little personal here, but I'm - I can't resist being a little bit personal. I would say that probably the most dramatic example is that my son, Matthew (ph) - his last name is Polan (ph) - his mother's last name was Polan. My last name is Pelham. And I entered a relationship with her before I developed this theory (laughter), not after I developed the theory to validate the theory.VEDANTAM: So you're a Pelham, and you got into a relationship with a woman named Polan.PELHAM: Polan - and we are very different in most other ways. That's about as much as I'll say about that (laughter).VEDANTAM: Are you saying that the names played some kind of a role?PELHAM: I have to think it did. I have to think - and we were from different backgrounds, different religions. I mean, we're - we come from very different worlds, yeah. And yet I was very attracted to her.VEDANTAM: So...PELHAM: And worse yet, she was attracted to me, right?VEDANTAM: Yeah (laughter). So I understand why you would sort of call this charming. And I think if you do this work for a while, there is a certain smile that comes to your face as you sort of look at these connections and you sort of see - you understand sort of the choices that human beings make.But I do think there's something disturbing about it because I think there is a very strong sense that I think most of us have. I have the sense, even though I've been covering the world of the unconscious mind for the last 10 years - I have the sense that my choices are deliberate choices, that I've thought about them, I've actually - I'm making them intentionally. And the idea that you're coming in and telling me that there are these hidden factors that come in and change how I think about myself - it is a disturbing idea.PELHAM: It is a little bit disturbing. And of course most people do what you and I do, which is say, well, of course, that applies to the rest of the world, but I in particular would never fall prey to implicit racial bias or implicit egotism. So most of us do tend to sort of separate ourselves from even our own findings. But I've become in the past decade or so comfortable enough with this idea that I have to admit that I really never know for sure exactly why I did something.I mean, sometimes, I have a pretty good idea, but I don't - I certainly don't kid myself anymore to say that I even usually know what - why I do what I do. I mean, there's just too much research, much of which you've documented and reported on that shows that biases we're completely unaware of nudge us, sometimes powerfully drive us in very particular directions. So I think I've just kind of let go of it. It was disturbing to me when I first began to study it (laughter) - disturbing as well as delightful. And now it's become more delightful and less disturbing.(SOUNDBITE OF MUSIC)VEDANTAM: So perhaps you're wondering, how does any of this matter? Who cares if people born on the 23 of September marry those born on the 23 of July? Who cares if someone named Betsy Carpenter gravitates towards carpentry? Why does it matter if I prefer a philosopher whose name is similar to my own?PELHAM: It at least raises tough questions about the degree to which we have free will. So I think some people who have pretty negative reactions to this work are very threatened by it in the sense that it suggests that very important decisions have at least a little nudging influence based on things that you're completely unaware of.So if people are more likely than they should be by chance to marry another person who happens to share their birthday number, that's not an objectively great reason to get married. You should get married because you share values, you're both Republicans, you're both rabid Marxists. But learning that these subtle little influences can affect what you do - apparently to some people it's - I find it delightful, but some people find it pretty threatening. I don't think that it proves that there's no such thing as free will. But it - to me, it does suggest that we don't always have free will. Sometimes we make a decision for one reason that we told ourself (ph) when really, the more powerful underlying reason is something we could've never put our fingers on.VEDANTAM: And this isn't just a matter of being drawn to someone who shares your birthday. In general, we tend to prefer things and people who have something to do with us, and that can be a big problem.PELHAM: Absolutely. I do a little bit of research on social justice, and that's one of the things that concerns me most - is that we tend to focus on people who are more like us, who speak our language, who speak our idiom, who look like us, who worship like us. And we pay much less attention, sadly, to the problems of people who don't. On the other hand, I think this finding, like any finding in psychology or behavioral economics, can be used for good or evil. And it - the way it works in the real world can be used for good or bad.And so a great example that I perceive as at least a cousin of implicit egotism is a study I think was done by Eliot Smith and colleagues about 10 years ago. He looked at implicit racial bias. And he looked at implicit racial bias as a function of whether a person from a different ethnic group - I think he had whites and African-Americans, for example - had simply given you a gentle, friendly touch on the shoulder. And if they had given you a friendly, gentle hello-how-are-you touch, that reduced their implicit racial bias.So to me, when another person becomes a part of you even in a very tiny way - you play intermural basketball with this person, and you didn't like his group. But now that you meet him and he's on your team, suddenly he becomes a part of you. His group becomes a part of you, and your stereotypes get softened and diminished a little bit.(SOUNDBITE OF MUSIC)VEDANTAM: If you can fall in love with your name or your birthday, can't you also fall in love with your own ideas, your own work? Of course you can. Researchers call this the Ikea effect.DANIEL MOCHON: Imagine that you built a table.VEDANTAM: This is Tulane University marketing professor Daniel Mochon.MOCHON: Maybe it came out a little bit crooked. Probably your wife or your neighbor would see it for what it is - you know, probably a shoddy piece of workmanship.VEDANTAM: A shoddy piece of workmanship because some of us are not necessarily talented at building our own furniture. In fact, if you go online, you can find plenty of videos of people struggling to put together their Ikea coffee table or dresser.(SOUNDBITE OF YOUTUBE VIDEO, "COUPLES RACE TO BUILD IKEA FURNITURE")UNIDENTIFIED MAN #4: I don't really understand what this part is. I don't feel like we have those pieces. We thought we did.VEDANTAM: But even though building the furniture can be a painful chore, people seem to really like the outcome.MOCHON: To you, that table might seem really great because you're the one who created it. It is the fruit of your labor, and that is really the idea behind the Ikea Effect. It is that we come to overvalue the things that we have created ourselves.VEDANTAM: In fact, this psychological bias might actually be an important part of Ikea's business model.MOCHON: The way people usually think about Ikea is that Ikea gives you good furniture for a low cost because they offload lots of the costs onto their consumers - the assembly costs. But in fact, we're in a sense challenging that idea and saying that there's actually a psychological benefit behind this, that actually people might end up liking their furniture more because they built it. And so it's not so much a cost but a benefit that they get to build their own furniture.VEDANTAM: Daniel and his co-authors did a series of experiments to test this hypothesis. They brought volunteers into the lab and gave them either a Lego car preassembled or gave them Legos and instructions and told the participants to build a car themselves. Then they asked the volunteers, how much would you pay to keep your Lego car?MOCHON: And what we find is that the people who build their own Legos not only are willing to pay more to keep their assembled Legos. But also when we ask them how proud they are of their own creations, they tend to be prouder of their Legos. And mind you, these are Legos that are designed to 5-to-7-year-olds. But nonetheless, there seems to be some competence, some pride associated with one's creation even for basic things as building Legos.VEDANTAM: The researchers replicated the study using other products like Ikea furniture, and the effect was the same. People who spent time and effort building something felt proud of what they'd built, fell in love with it and were willing to pay lots of money to keep the things they'd built. From the perspective of a rational economist, this doesn't make much sense.MOCHON: The students might be willing to pay twice as much money to buy the exact same Lego car if they just finished building that Lego car than if the Lego car was given to them pre-built.VEDANTAM: So why might people value something more after building it themselves compared to buying the same product made by someone else for half the cost?(SOUNDBITE OF MUSIC)MOCHON: Our hypothesis was that people tend to use products to signal value in identities to both themselves and to others. And we know that an identity that people really care about is showing that they are competent. This is sort of one of the basics of human motivation. And so we hypothesized that people use self-made products as a way to signal competence to both themselves and to others.You know, having just built a table or having just built a bookcase, that bookcase, that completed products acts in a sense of a badge of my own personal competence. I completed it, therefore I know I'm a competent person. And moreover, I can display this product and signal that identity, this competent identity to others. And so we hypothesized that it was these feelings of competence associated with the products that led to their increasing valuation.VEDANTAM: To test the theory that people's feelings of competence was behind the Ikea effect, the researchers had some participants think about other qualities they might value in themselves besides competence, things like honesty or intelligence or humor. Basically the idea was, if we make it less important for people to demonstrate competence, do they still overvalue their own creations?MOCHON: So we found that the Ikea effect disappeared when we did that manipulation. So once competence wasn't that important to people, people - our participants no longer seemed to get much value out of creating their own products, again, suggesting that the reason why we tend to like our own creations is because we use them as a way to signal competence both to ourselves and to others.VEDANTAM: Here's the flip side of that coin. You can make the Ikea effect stronger by getting people to question their competence. In one experiment, Daniel and his colleagues gave participants math problems to solve before asking them to build an Ikea project. If the problems were difficult, lots of people failed to solve them. Now volunteers became much more likely to want to demonstrate their competence through the Ikea building project.MOCHON: The participants who at least temporarily had their sense of competence threatened, who got the very difficult math questions tended to be more willing to build their own products. So when we surveyed them and asked them, would you prefer to have an Ikea product that comes pre-built or the exact same product that comes unbuilt and you would build it yourself, those who got difficult math problems and were feeling somewhat incompetent at the time seemed more willing. They were much more likely to want to build a product themselves and therefore, in a sense, restore their sense of competence through this activity.VEDANTAM: I mean, give me the numbers here. Was this a big effect? Was this a small effect? I mean, what happens when people feel bad compared to when they don't feel bad?MOCHON: So what we found is that about a third of the people wanted to build the Ikea bookshelf in the control condition when they weren't made to feel bad. And this number went up to about 60 percent when they were made to feel bad. So a significantly larger number of people wanted to do this.VEDANTAM: The Ikea effect and implicit egotism might seem at first blush to be interesting and amusing but not terribly significant. But the more I thought about this, the more I saw the potential implications. Just as we can be drawn to those who have the same birthday as us or the same name as us, we might also be more inclined to help people who look like us or sound like us or live near us.Let's say you're a congressperson who's drafted a particular piece of legislation. Your commitment to that bill might outweigh its importance to the public. Or let's say you're a president who starts a war. After years of investing your time and effort to prosecute that war, you may find it difficult to accept evidence that you made a mistake. It's fine to gaze lovingly in the mirror and to feel invested in our own ideas. But like Narcissus discovered himself, falling in love with our own reflection can come at great peril.(SOUNDBITE OF MUSIC)VEDANTAM: This week's show was produced by Maggie Penman and Parth Shah. It was edited by Tara Boyle. Our team includes Rhaina Cohen, Jenny Schmidt and Renee Klahr. Our engineers are Andy Huether and Jay Sciz (ph). NPR's vice president for programming and audience development is Anya Grundmann. You can also follow the show on Facebook, Twitter and Instagram and listen to my stories on Morning Edition each week on your local radio station. I'm Shankar Vedantam. See you next week.(SOUNDBITE OF MUSIC) Transcript provided by NPR, Copyright NPR.