That seems more like a testament to the intensity of someone who does X to be the "best" at it, rather than someone who does X for the fun of it. Go became more than just a game to him -- it was his identity.

For myself, I don't like to play online Go against humans, because I hate to lose. Instead, I play against a computer with a difficulty rating of around 1-3 dan, and whenever things start going badly for me I just undo moves and try again. Sometimes I ask the computer for advice on what move to make. My experience of Go is that I always win against a player who is much better than me. I find it pretty satisfying.

And yet there are millions of people that play Go who will never be anywhere close to as good as Lee and continue to play it after he quit.

It seems he based his ego on the idea of being the very best Go player, instead of merely being the best human Go player.