It is the pursuit of betterness in self that got me hooked on biking. For me biking is always a competition, but always against myself. It is a tangible measure of physical fitness and mental strength. Due to the multifaceted nature of biking I feel it is more capable of pushing oneself and building oneself than let's say simply running or weightlifting. In my biking I've enjoyed road, mtb, commuting, bike trials, and demos. Each has different areas that push you, build you, and can express you. The areas of your character and personality are built/changed differently by each aspect.
There is nothing like a full out sprint to absolute full end of your potential when you're actually in shape. Neither is there anything like cranking out 60 mile days... day after day after day. You look for that moment when you will collapse. Me and a friend in high school used to ride till be vomitted and keep on going, but we never raced for "real." It was a struggle to find who we were, what we were capable of. In trials I know to the inch what I can and cannot do, exactly where that line is... and I try to go just a little past it. It's also an art, a way to put one's self into a style or riding that is different than others. You become one with the bike, hands and feet don't end at pedals and handlebars. Your mind no longer thinks about how to do a bunnyhop... your nervous system has been programmed to do it automatically. It is beautiful and graceful and a continuation of self.
...Of course there are bad days when I can't focus or haven't ridden in a while