On any given Sunday. They don’t play the games on paper. These might be sport’s clichés, but they’re not wrong.

The perpetual center of our games is their always unpredictable nature. Spectator sports are the only true form of spontaneous entertainment we have left. And that sense of spontaneity, the feeling that at any given moment, anything can happen, lends much credence to a particular American value—that of infinite possibility.

Infinite possibility is the potential energy of spontaneity, the secret promise of sport. This is the idea that on any given Sunday David can slay Goliath. It’s the idea that an untested fifth round draft pick can lead a team of aging veterans to the Superbowl, as Tom Brady did in 2001. Anyone can be champion. Money doesn’t influence the outcome of the game and the reason the New York Yankees went to five of the last ten World Series has nothing to do with their also having the highest payroll in baseball. It’s the idea upon which this country is built: that anyone can rise to greatness, that every kid can play in the NBA, that we’re all potentially presidential material.

It helps explain why most of our sporting nation is currently rooting for the Atlanta Hawks.

The Hawks are the most improbable of stories: a mostly mediocre basketball team who backed into the playoffs with a sub-500 record. And for the first two games of their series with the seemingly unstoppable Boston Celtics they played about as well as one would expect: loosing the first two games (out of a best of seven series) by double-digits.

But something happened in Game 3 and that something has kept on happening in Game 4. Tonight, the Celtics will square off against the newly energized Hawks in a Game 5 that was never supposed to happen. And damn near every b-ball fan in the country will be cheering them on—but did you ever wonder why?

The psychology of the underdog has been a mostly unstudied phenomena until late last year, when a team led by University of South Florida psychologist Joseph Vandello, began exploring the reasons we cheer for the long shot.

Vandello looked not only at sports, but also at politics. For instance, in one study which used the Israeli-Palestinian conflict as an example, participants were given the same essay about the history of the area, but two different maps. One showing Palestine as smaller, the other a diminished Israel. In every case, subjects decided to side with the smaller—thus underdog—representation.

In fact, across the boards, no matter what the facts were, participants chose the underdogs to win.

As far as why? The researchers favor two ideas. The first is that cheering for those who are seen as disadvantaged seems to ignite our innate sense of fairness and justice. The second is the across-the-boards belief that the underdog needs to outwork the top dog in order to succeed.