Speed-dating has become enormously popular around the world over the last few years, and it’s not hard to understand why. It’s the distillation of dating to a simple snap judgment. Everyone who sat down at one of those tables was trying to answer a very simple question: Do I want to see this person again? And to answer that, we don’t need an entire evening. We really need only a few minutes. Velma, for instance, one of the four Anne Klein women, said that she picked none of the men and that she made up her mind about each of them right away. “They lost me at hello,” she said, rolling her eyes. Ron, who worked as a financial analyst at an investment bank, picked two of the women, one of whom he settled on after about a minute and a half of conversation and one of whom, Lillian at table two, he decided on the instant he sat down across from her. “Her tongue was pierced,” he said, admiringly. “You come to a place like this and you expect a bunch of lawyers. But she was a whole different story.” Lillian liked Ron, too. “You know why?” she asked. “He’s from Louisiana. I loved the accent. And I dropped my pen, just to see what he would do, and he picked it up right away.” As it turned out, lots of the women there liked Ron the instant they met him, and lots of the men liked Lillian the instant they met her. Both of them had a kind of contagious, winning spark. “You know, girls are really smart,” Jon, a medical student in a blue suit, said at the end of the evening. “They know in the first minute, Do I like this guy, can I take him home to my parents, or is he just a wham-bam kind of jerk?” Jon is quite right, except it isn’t just girls who are smart. When it comes to thin-slicing potential dates, pretty much everyone is smart.

But suppose I were to alter the rules of speed-dating just slightly. What if I tried to look behind the locked door and made everyone explain their choices? We know, of course, that that can’t be done: the machinery of our unconscious thinking is forever hidden. But what if I threw caution to the winds and forced people to explain their first impressions and snap judgments anyway? That is what two professors from Columbia University, Sheena Iyengar and Raymond Fisman, have done, and they have discovered that if you make people explain themselves, something very strange and troubling happens. What once seemed like the most transparent and pure of thin-slicing exercises turns into something quite confusing.

Iyengar and Fisman make something of an odd couple: Iyengar is of Indian descent. Fisman is Jewish. Iyengar is a psychologist. Fisman is an economist. The only reason they got involved in speed-dating is that they once had an argument at a party about the relative merits of arranged marriages and love marriages. “We’ve supposedly spawned one long-term romance,” Fisman told me. He is a slender man who looks like a teenager, and he has a wry sense of humor. “It makes me proud. Apparently all you need is three to get into Jewish heaven, so I’m well on my way.” The two professors run their speed-dating nights at the back of the West End Bar on Broadway, across the street from the Columbia campus. They are identical to standard New York speed-dating evenings, with one exception. Their participants don’t just date and then check the yes or no box. On four occasions—before the speed-dating starts, after the evening ends, a month later, and then six months after the speed-dating evening—they have to fill out a short questionnaire that asks them to rate what they are looking for in a potential partner on a scale of 1 to 10. The categories are attractiveness, shared interests, funny/ sense of humor, sincerity, intelligence, and ambition. In addition, at the end of every “date,” they rate the person they’ve just met, based on the same categories. By the end of one of their evenings, then, Fisman and Iyengar have an incredibly detailed picture of exactly what everyone says they were feeling during the dating process. And it’s when you look at that picture that the strangeness starts.

For example, at the Columbia session, I paid particular attention to a young woman with pale skin and blond, curly hair and a tall, energetic man with green eyes and long brown hair. I don’t know their names, but let’s call them Mary and John. I watched them for the duration of their date, and it was immediately clear that Mary really liked John and John really liked Mary. John sat down at Mary’s table. Their eyes locked. She looked down shyly. She seemed a little nervous. She leaned forward in her chair. It seemed, from the outside, like a perfectly straightforward case of instant attraction. But let’s dig below the surface and ask a few simple questions. First of all, did Mary’s assessment of John’s personality match the personality that she said she wanted in a man before the evening started? In other words, how good is Mary at predicting what she likes in a man? Fisman and Iyengar can answer that question really easily, and what they find when they compare what speed-daters say they want with what they are actually attracted to in the moment is that those two things don’t match. For example, if Mary said at the start of the evening that she wanted someone intelligent and sincere, that in no way means she’ll be attracted only to intelligent and sincere men. It’s just as likely that John, whom she likes more than anyone else, could turn out to be attractive and funny but not particularly sincere or smart at all. Second, if all the men Mary ends up liking during the speed-dating are more attractive and funny than they are smart and sincere, on the next day, when she’s asked to describe her perfect man, Mary will say that she likes attractive and funny men. But that’s just the next day. If you ask her again a month later, she’ll be back to saying that she wants intelligent and sincere.

You can be forgiven if you found the previous paragraph confusing. It is confusing: Mary says that she wants a certain kind of person. But then she is given a roomful of choices and she meets someone whom she really likes, and in that instant she completely changes her mind about what kind of person she wants. But then a month passes, and she goes back to what she originally said she wanted. So what does Mary really want in a man?

“I don’t know,” Iyengar said when I asked her that question. “Is the real me the one that I described beforehand?”

She paused, and Fisman spoke up: “No, the real me is the me revealed by my actions. That’s what an economist would say.”

Iyengar looked puzzled. “I don’t know that’s what a psychologist would say.”

They couldn’t agree. But then, that’s because there isn’t a right answer. Mary has an idea about what she wants in a man, and that idea isn’t wrong. It’s just incomplete. The description that she starts with is her conscious ideal: what she believes she wants when she sits down and thinks about it. But what she cannot be as certain about are the criteria she uses to form her preferences in that first instant of meeting someone face-to-face. That information is behind the locked door.

Braden has had a similar experience in his work with professional athletes. Over the years, he has made a point of talking to as many of the world’s top tennis players as possible, asking them questions about why and how they play the way they do, and invariably he comes away disappointed. “Out of all the research that we’ve done with top players, we haven’t found a single player who is consistent in knowing and explaining exactly what he does,” Braden says. “They give different answers at different times, or they have answers that simply are not meaningful.” One of the things he does, for instance, is videotape top tennis players and then digitize their movements, breaking them down frame by frame on a computer so that he knows, say, precisely how many degrees Pete Sampras rotates his shoulder on a cross-court backhand.