Overconfidence can also vary significantly. Men tend to be more overconfident than women (although some studies suggest this isn’t always the case). Americans are more overconfident than East Asians. As two psychologists put it, “Americans are widely regarded as the most optimistic people on earth.” Elites are more prone to overconfidence, whether they’re top-class chess players or masters of the universe on Wall Street.

Given all this, Donald Trump seems almost uniquely likely to succumb to hubris. Not only is he male, American, and a member of the elite (for all his talk of populism), but he also instinctively responds to challenges by coming out swinging, and is prone to narcissistic or arrogant behavior, such as declaring he doesn’t need daily intelligence briefings, where he says he would hear “the same thing in the same words every single day.” At different times, Trump has retweeted a quote from Benito Mussolini (“It is better to live one day as a lion than 100 years as a sheep”) and lauded Saddam Hussein (“you know what he did well? He killed terrorists”)—two autocrats known for their self-destructive overconfidence.

The initial months of a Trump presidency present particular risks of hubris. Early on, presidents may be tempted by wild adventures, before the realities of office temper their hopes and dreams. Soon after taking the oath of office, JFK gave the green light to the outlandishly flawed Bay of Pigs invasion. George W. Bush espoused missionary crusading zeal after 9/11, but cut a more chastened figure in his second term.

Overconfidence can be a useful trait in some ways, by encouraging leaders to persevere in the face of obstacles. But illusions of triumph can also lead to catastrophic decisions like the invasion of Iraq, where officials predicted that U.S. troops would be greeted as liberators, and neglected the chances of disorder or insurgency following regime change. A RAND study found that in pre-war analyses: “post conflict stabilization and reconstruction were addressed only very generally, largely because of the prevailing view that the task would not be difficult.”

What if Trump encounters an unexpected foreign-policy crisis in the early months of his administration? What if North Korea launches a fresh provocation? What if Trump deploys larger numbers of military forces to the Middle East to combat jihadi terrorists?

It is difficult or impossible to self-regulate against overconfidence. Ironically, a classic example of positive illusions is that people believe they are better than their peers at seeing things accurately, uncontaminated by overconfidence.

The most effective way to check hubris is to empower outsiders, such as a board of directors who can hold a CEO accountable. Trump doesn’t have a board, but he does have a Cabinet. Trump once said that he might not come to the aid of NATO allies. Senate Majority Leader Mitch McConnell seemed unworried because Trump’s advisers would take a different perspective. “I don’t think that view would be prevalent or held by anybody he might make secretary of state or secretary of defense.”