They happen in all sports.
But there are upsets and then there are UPSETS, which is why Rafael Nadal's second-round loss at Wimbledon in July ranks right up there with Maria Sharapova's career Grand Slam and Andy Murray's victory at the U.S. Open as a moment of the year -- for me, it's not just THE moment of the year, it's a moment for the years.
My choice hinges on a number of factors. Not just because it was unexpected (isn't every upset so?). This was as unexpected as Tim Tebow suddenly declaring he's an atheist or even Chad Johnson answering a question with " no comment."
Before Lukas Rosol, the 26-year old Czech and No. 100 player in the world, bounced Nadal out of Wimbledon, the Spanish star had lost exactly three matches in more than seven years at the world's most closely watched tournament.
One of those losses was in 2011, to world no. 1 Novak Djokovic in the midst of his career year. The other two, dating back to 2006, were both to Roger Federer, who was in the midst of serial career years that left him the all-time singles Grand Slam champion.
And that's not all.
The only two other losses Nadal suffered at Wimbledon were to Thai player Paradorn Srichapan in 2003 (Nadal had just turned 17) and in 2005 to Luxembourg's Gilles Muller. Srichapan was ranked No. 11 at the time; Muller was No. 69, and a little closer to the kind of big hitter that can make Wimbledon such a perilous experience for a baseliner.
But it wasn't just that Nadal lost to an ATP outlier. The match conditions were such that Nadal got just the kind of break that others in his position have capitalized on over the years. That was the decision to close the Centre Court roof in the fourth set -- one during which he seemed to find his A-game again as he swept it, 6-2.
Remember how the rain delay during the 1991 French Open final enabled Jim Courier to conspire with his coach and, when the match resumed, turn the tables and beat Andre Agassi?
Nadal fans will forever say that the break in the momentum (the closing of the roof and activation of the critical "moisture control" system takes about 45 minutes) cost him the match.
But my feeling is that such interruptions almost always work against the underdog, especially if it's a generally high-quality match and the lesser player (Rosol) has been in the proverbial "zone."
The break gives the favorite the opportunity to regroup and think through the remaining task -- something top players are accustomed to doing, given their familiarity with big-match conditions.
The underdog, meanwhile, has to worry about losing that magical touch. He has to be somewhat anxious about retaining the form that eludes him in almost every match he plays, and he has to face numerous self-imposed questions, starting with the simplest of them all: "Am I really capable of pulling this off?"
Followed by: "Should I keep doing what I'm doing, or maybe dial it back a bit, just to be in the safe side (usually, that's the kiss of death)"?
And lastly, a winner-take-all fifth set is familiar territory for a multiple Grand Slam champion. But it's a nerve-wracking test for a guy who, to borrow a pharse, has a funny feeling he's not in Kansas anymore.
Rosol put on an astonishing display of firepower in the fifth set under the roof of Centre Court, and there wasn't a darned thing Rafael Nadal could do about it -- not even if he handed his racquet to Federer, or Djokovic. Rosol's upset was an astonishing performance that was not just the most electric moment of the year, it was an upset that immediately entered the lore and legend of the game.