Every March Madness features all sorts of thrilling upsets. No. 14 seeds knocking off No. 3 seeds. Overmatched teams beating dominant ones.

These upsets are why so many sports fans watch and love the NCAA tournament. Unlike other sports' playoffs, it pits underdog teams from small schools against powerhouse behemoths — and, with surprising frequency, the underdogs win.

But it all raises a bigger question: why do we love these upsets in the first place? Why do we have such a strong urge to root for the underdog?

Scientists have found our love for the underdog is quite real

A few different psychology researchers have looked into our love for the underdog, and they've found that it's pervasive.

This phenomenon can cause people to switch their allegiances between teams in a single series — just based on who's up and who's done. In one study, people who read descriptions of two fictional basketball teams playing each other in a seven-game series rooted for the team described as the underdog 88.1 percent of the time. But when these people were told that the favorite unexpectedly lost the first three games of the series — putting them on the brink of elimination and making them the new underdog — about half changed their allegiance.

in one study, 88.1 percent of people rooted for the underdog

This effect has also been observed in people watching actual basketball games. In another study, American college students watched a game between European teams, and were told that either one team or the other had won the last 15 games between them. Again, they consistently rooted for underdog to spring an upset, whichever team it was.

The phenomenon has also been documented outside sports. In one 1980 study — conducted during the presidential election — participants disproportionately rooted for Ronald Reagan when told that Jimmy Carter had a lead in the polls, and rooted for Carter when told that Reagan did.

Theory 1: We root for underdogs because of schadenfreude

One theory, put forth by UC San Diego researcher Nadav Goldschmied, is that our love for the underdog is basically an expression of schadenfreude — pleasure we experience due to the misfortune of others. We resent powerhouse teams that win every year, the thinking goes, so we root for them to lose.

It seems logical, but evidence for the idea is mixed. In Goldschmied's experiments, participants actually rooted for underdogs slightly less when told that their victory would knock the favored team out of the playoffs (in sports, a team winning here is often called a "spoiler"). This suggests the participants weren't actually rooting for misfortune so much as unexpected triumph.

In another experiment, though, Goldschmied told participants that the favored team spent way more on its payroll — and it dramatically boosted support for the underdog, compared with when the teams spent similarly. This provides support for the schadenfreude idea, and could be the reason so many people love to hate the Yankees: there's something great about watching a team that's spent so much money go down.

Theory 2: We want the world to be just

Another way to interpret this result is that deep down, we want the world to be fair. Some teams — whether pro or college — can pour more money into winning, but we want everyone to have an equal shot at it, and when upsets happen, it tells us they do.

Good evidence for this idea comes from another study conducted by Goldschmied, along with Joseph Vandello of the University of South Florida. It also involved a hypothetical matchup between two teams: one that had a good chance of winning, and one that had a small chance. But here, in some cases, the researchers told participants that the latter team actually spent a lot more money.

When that happened, people no longer labeled them "underdogs" and didn't root for them to win. Something about the underdog identity, it seems, has to do with "deserving" to win against the odds. If you have more money and still have little chance of winning, the thinking goes, that's just your fault.

Theory 3: We don't want to get our hopes up

Psychologists consistently find that people get more joy out of unexpected successes than expected ones, and similarly experience more pain from unexpected failures than ones we anticipate. Some researchers point out that this could provide a good reason to root for the underdog: you have less to lose if your team loses, and a lot more to gain if it pulls off an upset.

No one has specifically studied this idea as it relates to rooting for underdogs, though, and it's hard to say whether it really applies. This sort of thinking is a very calculated, rational way to approach a game — and there's something emotional and uncontrolled about many people's love for the upset.

The limits of our love for the underdog

It's easy to root for the underdog and the upset when there's little at stake — but when we have something real to lose, researchers find, our support tapers off.

Scott Allison of the University of Richmond came to this conclusion in a study on people's support for all sorts of underdogs, whether in sports, business, or art. In one part of the study, participants read a scenario in which two companies competed for a contract to to test the water in Boise, Idaho.

when there's something real to lose, our support tapers off

One was a new, struggling, small company, the other a well-established, decades-old one. When asked, slightly more than half of participants said they'd root for the small one to land the contract. But when the scenario was changed so that participants were told the companies would be testing water for potential cancer-causing chemicals in their own hometowns, the results were the opposite: more than twice as many rooted for the established, reliable company to win the bid.

The conclusion Allison draws is that when we have something bigger on the line — in this case, health — our support for the underdog evaporates. Similarly, he writes, we might root for a mom-and-pop store when Walmart moves in to the neighborhood, but ultimately we make big purchases wherever it's cheaper.

In sports, this is expressed in the fact that most of us root for upsets — unless they come at the expense of our own team. Ultimately, our team winning is the priority, and upsets are a thrilling, secondary interest. As Allison puts it, "Although rooting for the underdog is pervasive, the effect is a mile wide and an inch deep."