Another worthwhile passage from Lou Holtz's autobiography:
Every athlete who has ever played for me has heard me preach against the pitfalls of entering anything halfway. In my mind, a half-hearted commitment is worse than no commitment at all.
If you decide to take a class, you should give the professor and yourself the full benefit of your undivided attention. If you don't, you're wasting your time and taking up a valuable seat in the classroom.
If you're on a team, you owe your coaches and your teammates your total commitment. If you don't -- if you're unhappy because the coach doesn't start you, or because you aren't getting as many touches as you think you should -- you are hurting yourself and the entire organization. You and the team would be better off if you played somewhere else.
Commitment is the most critical component in any relationship. In sports, it's become axiomatic: Commitment beats talent every time.