I know this thread is about pool, but I think one of the all time saddest stories of someone who quit young in any game/sport is Bobby Fischer, the American chess player.
For those who don't know the story, at the time Bobby made his meteoric rise through American chess, America was not the place you wanted to grow up as a chessplayer, much like modern America and pool. America did not support Bobby at all, and he had to fight for funding from the US Chess Federation in order to compete internationally. A lot of times, he competed by getting donations from the chess community.
Russians ruled international chess. Bobby taught himself Russian in order to read their chess manuals. Bobby, however, suffered from increasing paranoia and mental instability. His requests during competition became more and more burdensome.
He won the World Championship over Boris Spassky, then immediately retreated from the chess scene. After withdrawing from his friends, Bobby became more and more unstable, until he ended up on Filipino radio spouting anti-Semitic comments to the world.
It just doesn't get any more tragic than this. He was a generation's symbol of defiance towards the communist threat from Russia. It gave so many hope to see one American man, through sheer brilliance, defeat the Soviet chess machine that had been churning out world champions for decades.. Bobby Fischer was a superstar whose popularity in those days, probably eclipsed many of the major movie stars of the day. For those who never saw any pictures of him, he was an extremely handsome man, and at the height of his popularity, if he wasn't so shy, would have had his pick of women from any strata of society. That's the beauty of being the best chess player in the world, young, handsome, and charismatic.. Unfortunately.. He was also extremely shy around women. His charisma was mainly devoted to talking about chess. Like Warren Buffet, Bobby had so much enthusiasm about his chosen profession, that he could fascinate you with an intrinsicly boring subject.
To see a man with that much talent descend into insanity in such a public way has been a hard blow on the entire international chess community. When Bobby played a rematch against Spassky in the 90's, even the Russians were anticipating seeing if the brilliance of Fischer had held through the years. Sadly, it had not. He played at a "mediocre" (for an International GrandMaster) level.
Bobby's best days were far far behind him.
Sorry for taking the thread off topic, but I felt that I have rarely seen any story of lost potential as sad as Fischer's..
Russ