Let me tell you about a classic psychological study that I don't believe. In the early 1980s, Amos Tversky and Thomas Gilovich began sifting through years of statistics from the Philadelphia 76ers. The psychologists looked at every single shot taken by every single player, and recorded whether or not that shot had been preceded by a string of hits or misses. All told, they analyzed thousands upon thousands of field goal attempts.

Why'd they do this? Tversky and Gilovich were interested in testing the "hot hand" phenomenon, which occurs when NBA players are convinced that they're hot, on a roll, in the zone. (The sports cliches are endless.) While players, coaches and spectators were convinced the hot hand was real, the psychologists knew that humans are notoriously bad at detecting streaks. After all, we're the same species that gets convinced we're playing a "hot" slot machine.

After analyzing all the shots of the 76ers, the psychologists discovered that there was absolutely no evidence of "the hot hand." A player's chance of making a shot was not affected by whether or not their previous shots had gone in; each field goal attempt was its own independent event. The short runs experienced by the 76ers were no different than the short runs that naturally emerge from any random process. Taking a jumper was like flipping a coin. The streaks were a figment of our imagination.

The 76ers were shocked by the evidence. Andrew Toney, the shooting guard, was particularly hard to convince: he was sure that he was a streaky shooter, and went through distinct "hot" and "cold" periods. (Toney is still regarded as a great clutch player. Charles Barkley has called him "one of the best kept secrets in the history of the NBA.") But the statistics told a different story. During the regular season, Toney made 46 percent of all of his shots. After hitting three shots in a row - a sure sign that he was now "in the zone" - Toney's field goal percentage dropped to 34 percent. When Toney thought he was "hot," he was actually freezing cold. And when he thought he was cold, he was just getting warmed up: after missing three shots in a row, Toney made 52 percent of his shots, which was significantly higher than his normal average.

But maybe the 76ers were a statistical outlier. After all, according to a survey conducted by the scientists, 91 percent of serious NBA fans believed in "the hot hand". They just knew that players were streaky. So Tversky and Gilovich decided to analyze another basketball team: the Boston Celtics. This time, they looked at free throw attempts, and not just field goals. Once again, they found absolutely no evidence of hot hands. Larry Bird was just like Andrew Tooney: After making several free throws in a row, his free throw percentage actually declined. Bird got complacent, and started missing shots he should have made.

Why, then, do we believe in the hot hand? Confirmation bias is to blame. Once a player makes two shots in a row - an utterly unremarkable event - we start thinking about the possibility of a streak. Maybe he's hot? Why isn't he getting the ball? It's at this point that our faulty reasoning mechanisms kick in, as we start ignoring the misses and focusing on the makes. In other words, we seek out evidence that confirms our suspicions of streakiness. The end result is that a mental fiction dominates our perception of the game.

Here's where things get meta: Even though I know all about Tversky and Gilovich's research - and fully believe the data - I still perceive the hot hand. I can't help but watch the NBA playoffs and marvel at the streakiness of shooters, from Kobe to Rose. (Personally, I'd love to see an analysis of Ray Allen. If that man doesn't show the hot hand, then it really doesn't exist.) And I'm not alone in my stubborn skepticism. Red Auerbach, the legendary coach of the Celtics, reportedly responded to Tversky’s statistical analysis with a blunt dismissal. “So he makes a study,” Auerbach said. “I couldn’t care less.”

The larger question, of course, is why confirmation bias exists. This is the sort of mental mistake that seems ripe for fixing by natural selection, since it always leads to erroneous beliefs and faulty causal theories. We'd be a hell of a lot smarter if we weren't only drawn to evidence that confirms what we already believe.

And this leads me to a fascinating and provocative new theory of reasoning put forth by Hugo Mercier and Dan Sperber. In essence, they argue that human reason has nothing to do with finding the truth, or locating the best alternative. Instead, it’s all about being able to argue with others:

Reasoning is generally seen as a mean to improve knowledge and make better decisions. Much evidence, however, shows that reasoning often leads to epistemic distortions and poor decisions. This suggests rethinking the function of reasoning. Our hypothesis is that the function of reasoning is argumentative. It is to devise and evaluate arguments intended to persuade.

In the most recent edition of Edge.org, there's a great conversation with Mercier, now a post-doc at Penn. Mercier begins by explaining how the argumentative theory of human reason can explain confirmation bias:

Psychologists have shown that people have a very, very strong, robust confirmation bias. What this means is that when they have an idea, and they start to reason about that idea, they are going to mostly find arguments for their own idea. They're going to come up with reasons why they're right, they're going to come up with justifications for their decisions. They're not going to challenge themselves. And the problem with the confirmation bias is that it leads people to make very bad decisions and to arrive at crazy beliefs. And it's weird, when you think of it, that humans should be endowed with a confirmation bias. If the goal of reasoning were to help us arrive at better beliefs and make better decisions, then there should be no bias. The confirmation bias should really not exist at all. But if you take the point of view of the argumentative theory, having a confirmation bias makes complete sense. When you're trying to convince someone, you don't want to find arguments for the other side, you want to find arguments for your side. And that's what the confirmation bias helps you do. The idea here is that the confirmation bias is not a flaw of reasoning, it's actually a feature. It is something that is built into reasoning; not because reasoning is flawed or because people are stupid, but because actually people are very good at reasoning — but they're very good at reasoning for arguing. Not only does the argumentative theory explain the bias, it can also give us ideas about how to escape the bad consequences of the confirmation bias.

Needless to say, this new theory paints a rather bleak portrait of human nature. We like to think of ourselves as rational creatures, blessed with this Promethean gift of being able to decipher the world and uncover all sorts of hidden truths. But Mercier and Sperber argue that reason has little to do with reality, which is why I'm still convinced that those NBA players are streaky when they're really just lucky. Instead, the function of reasoning is rooted in communication, in the act of trying to persuade other people that what we believe is true. We are social animals all the way down.