“Our model shows that all you really need is false beliefs about yourself,” said James Fowler, a social scientist at the University of California, Davis. “When you’re bluffing, you make statements like, ‘I’m going to kick your butt.’ We’re not talking about this kind of trash talk here. This is internal.”

“Muhammad Ali always talked about being the ‘greatest fighter in the world,'” he added. “I’m sure his internal belief that he was that person contributed to him becoming that person.”

In study after study, researchers have documented that overconfidence is widespread. In one survey, 94 percent of college professors said their teaching skills were above average — echoing Garrison Keillor’s Lake Wobegon effect, in which “all the women are strong, all the men are good-looking and all the children are above average.” In another study, 70 percent of high-school students rated their leadership skills as higher than normal. Other studies have shown that men often over-estimate their attractiveness.