One of the things that happen to us when we become overconfident is that we start to blur the line between the kinds of things that we can control and the kinds of things that we can’t. The psychologist Ellen Langer once had subjects engage in a betting game against either a self-assured, well-dressed opponent or a shy and badly dressed opponent (in Langer’s delightful phrasing, the “dapper” or the “schnook” condition), and she found that her subjects bet far more aggressively when they played against the schnook. They looked at their awkward opponent and thought, I’m better than he is. Yet the game was pure chance: all the players did was draw cards at random from a deck, and see who had the high hand. This is called the “illusion of control”: confidence spills over from areas where it may be warranted (“I’m savvier than that schnook”) to areas where it isn’t warranted at all (“and that means I’m going to draw higher cards”).

Most people are inclined to use moral terms to describe overconfidence—terms like “arrogance” or “hubris.” But psychologists tend to regard overconfidence as a state as much as a trait. Langer didn’t say that it was only arrogant gamblers who upped their bets in the presence of the schnook. She argues that this is what competition does to all of us; because ability makes a difference in competitions of skill, we make the mistake of thinking that it must also make a difference in competitions of pure chance. Other studies have reached similar conclusions. As novices, we don’t trust our judgment. Then we have some success, and begin to feel a little surer of ourselves. Finally, we get to the top of our game and succumb to the trap of thinking that there’s nothing we can’t master. As we get older and more experienced, we overestimate the accuracy of our judgments, especially when the task before us is difficult and when we’re involved with something of great personal importance.

This is what social scientists mean when they say that human overconfidence can be an adaptive trait. “In conflicts involving mutual assessment, an exaggerated assessment of the probability of winning increases the probability of winning,” Richard Wrangham, a biological anthropologist at Harvard, writes. “Selection therefore favors this form of overconfidence.” Winners know how to bluff. And who bluffs the best? The person who, instead of pretending to be stronger than he is, actually believes himself to be stronger than he is. According to Wrangham, self-deception reduces the chances of “behavioral leakage”; that is, of “inadvertently revealing the truth through an inappropriate behavior.” This much is in keeping with what some psychologists have been telling us for years—that it can be useful to be especially optimistic about how attractive our spouse is, or how marketable our new idea is. In the words of the social psychologist Roy Baumeister, humans have an “optimal margin of illusion.”