One of the basic appeals of sports is that the impossible is constantly being made possible. The fact that something has never occurred is precisely the reason you should look forward to it. Eventually, someone or some team breaks through.

The NCAA tournament's primary sales point is that anyone can win it: It's the most underdog-friendly massive event in sports. The whole premise has that baked in. When we think of the tournament, we think of the big moments, sure: Christian Laettner's shot against Kentucky, Michael Jordan's shot against Georgetown. But more so, we think about the small schools emerging on the grandest possible stage, coming out of nowhere and shocking the world. The big schools, at least at the beginning of the tournament, hold far less fascination: It's not exciting if Arkansas beats Iowa. But when Lehigh takes out Duke in the first round, the earth shakes beneath us. That moment, late in the second half, when it becomes clear that an upset-minded team has a real chance here, is as thrilling as anything in sports. It's what the tournament is about.

But the biggest upset of all… that's the one we're still waiting on.

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Last year, the NCAA tournament's biggest upset featured those crazy Dunk City kids of Florida Gulf Coast -- the Dunk City was Fort Myers, a city that has to be one of the least dunk-ish in the United States -- taking out Georgetown and ultimately advancing to the Sweet 16. I was fortunate enough to be at Wells Fargo Center in Philadelphia, and it was as wild a party as I can remember at a college basketball game. Florida Gulf Coast, a No. 15 seed, couldn't have had a more supportive fanbase if it had been playing exclusively in front of friends, family and people who owed it money. Florida Gulf Coast fans -- and I actually found one -- had the ultimate tournament experience.

And it wasn't all that rare. In the last two years, three No. 15 seeds have advanced to the round of 32: Florida Gulf Coast last year, and Lehigh (over Duke) and Norfolk State (over Missouri) in 2012. (FGCU was the first No. 15 seed to reach the Sweet 16.) Last year, for the first time, a 15, 14, 13, 12 and 11 seed all won. Here are the number of times a lower seed has won since 1985:

11 seed: 39 times
12 seed: 41 times
13 seed: 25 times
14 seed: 17 times
15 seed: 7 times

Which brings us to the No. 16 seed: 0 times.

It's the one upset we all want to see the most. It would instantly become the most iconic early-round moment in tournament history. It would make Dunk City look like an NAIA game.

But when will it actually happen?

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The most famous No. 16 vs. No. 1 game was the 50-49 Georgetown win over Princeton in 1989. Princeton had a chance to win on the last possession of the game, but Alonzo Mourning blocked two shots to secure the victory and leave Pete Carril just short of a moment that would live forever. That same year, a No. 16 seed would come close again: East Tennessee State would miss a long shot at the buzzer to lose to Oklahoma.

There have been occasional scares since then. The great Illinois team of Deron Williams/Dee Brown/Luther Head led Fairleigh Dickinson by only one at the half in 2005. Michigan State needed overtime against Murray State in 1990. Purdue snuck away with a two-point win over Western Carolina in 1996. UNC Asheville landed a few punches against Syracuse a couple of years ago, and some of their fans are still sore about the officiating at the end of that game.

It's getting closer to happening. Last year, Louisville beat North Carolina A&T by 31, and Indiana beat James Madison by 21. But the other two were a little tighter: Kansas beat Western Kentucky by only seven, and Gonzaga sweated out a six-point win over Southern. (And then lost in the next round to eventual Final Four team Wichita State.) There have been a total of 14 16-vs.-1 games decided by fewer than 10 points, and three have happened in the last two years.

This fits with the general trends of the game. The top-tier teams, thanks to attrition, early exits and transfers, aren't as top-tier as they used to be; you don't get three future NBA prospects playing together as upperclassmen anymore. The talent level across college basketball is more spread out than it used to be. The difference between the top teams and the mid-majors isn't as dramatic, as evidenced by Wichita State, this year and last. Also, the three-point line has been a grand equalizer too; we love the tournament for the randomness that comes when an inferior team just gets hot at the right time. This primes the pump for a No. 16 upset: on any given night.

Fifteen-seeds are winning at an exponentially high rate. Parity has taken over college basketball. It has to happen at some point. And it's likely going to happen soon.

We don't know who the No. 1 seeds are going to be this year yet, though Florida and Wichita State seem like locks, with Arizona, Villanova, Kansas and Wisconsin/Michigan right behind them. We can have a solid idea of who the No. 16 seeds are going to be: Wisconsin-Milwaukee (who finished fifth in the Horizon League), Utah Valley (who is favorite in the wretched WAC), Mount St. Mary's and whoever wins the SWAC are the most likely nominees. Of course, now, No. 16 seeds have to play a game just to make it into the 64-team bracket, which theoretically should help them: You're less likely to be overwhelmed when you've already won one game in the tourney. (Particularly if the president was watching.)

It likely won't go down this year; the odds are perpetually against it. A study a few years ago argued that a No. 16 seed had a 1-in-54 chance of winning a given game. That number has surely gone down since then, but 1-in-54 for any 16-seed to win means roughly a 6.25 percent chance that one of the four No. 16 seeds will do it. It also means that it's statistically improbable that it hasn't happened before now. It means it's only a matter of time.

And it when it does happen, it'll be the culmination of countless trends, the next step in great democratization of college basketball. Mostly, though, it will be the biggest story in sports. It'll be someone. The only questions are who -- and when. It could be this year. It could be any year. But it will be one year.

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Email me at leitch@sportsonearth.com; follow me @williamfleitch; or just shout out your window real loud, I'll hear you. Point is, let's talk.