I have tried to explain myself many times but it always comes up short. When George Mallory said in response to why he wanted to climb Everest he said "Because it's there." In a world of never ending tests and research and relationships that go up and down and get nowhere climbing a mountain or finishing a race is so definitive. They are an end in themselves. Completion of something that took a lot of effort. After banging my head against my research and differential equations the mental energy required to push myself from 51 miles to 52 miles is like a vacation. It's so simple: just go forward. The physical pain is also really comforting because it's real.
Am I crazy? I think about that a fair amount. Probably more than most people. Most of the time I decide that if I have to ask the question and think about it then I'm probably not crazy. Actually one of my greatest fears is that when they are doing all of the tests for the crew to Mars I won't make it because I'm too crazy for NASA. I also know that if things continue at their current rate I'm just going to get more crazy by the world's definition.
What I'm trying to say is that there are things I do and want to do that are painful, scary, dangerous, time-consuming, profitless, committing, and I do them in part for those reasons but also to know what it's like. If you want to feel why I do them then come with me on an adventure. Otherwise, go ahead and call me crazy.