Why do you race?

My good friend Janelle Smiley and I managed to grab a quick bite to eat last week before her an her husband headed off on a climbing trip in AK. Over teocolli tamale burritos we had a great conversation about why we race.  Janelle, even as reigning US National Ski Mountaineering champion might have the best perspective of anyone I know.
So as I headed into my first mountain bike race of the season in Rabbit Valley(Fruita) this past weekend the question was fresh in my mind.  Why do I race? Is it the challenge? My ego? to win?  I spent a considerable amount of time in the race pondering this question, but with no clear answer. 
So, I'm curious, why do YOU race?