It's -3, pi$$ing it down, I've had no food for the last two hours, soaked to the skin, shivering, and I have to mend a puncture with fingers I can't feel and then get the last 30 miles home. I ask myself that sometimes.
Then it's 25 degrees, I've got the sun on my back, a big cloud of dust behind me as I swoop down the cut-gate, hitting every turn to perfection, every braking point spot-on, and then I have my answer.
Also, what Steveh said, I have based my life for the last decade around riding and racing bikes. About this time yesterday I was halfway through a 2hr phone call to my (now ex) girlfriend going through the most painful breakup ever, too much time riding was part of the reason (amongst others) but I can't change. If I did, I'd resent doing it and that's never going to keep a relationship alive. I don't know how it's happened but riding has become my life.