Jason Scully breaks down some great pointers about competing. I don't think you need to be a grappler to appreciate his points and lessons, as they apply to anyone who pushes their comfort zone and puts it all on the line just for the sake of putting on the line. Keep in mind that regardless of the activity we compete in, the overwhelming majority of us (I would say 95%) do not make a penny competing. As a matter of fact we SPEND tons of dinero every year just to go out on the mat, or the shooting range, or the track, or the field.... just to push ourselves to new limits in an effort to learn and grow as competitors, as well as human beings.
Jason lays it out much smoother and more organized than I could have. But I think this pretty much summarizes why I, and many others compete.