It depends on the subject. If it’s your marriage, you need to do everything possible to make it a life-long covenant relationship. If it is your job, or some other endeavor, there needs to be a way to know when to say, “when.”
We wouldn’t want to quit too soon. I heard a radio commentator say that John Edwards is probably kicking himself right now for getting out of the presidential race when he did. Maybe he quit too soon. Most of us don’t want to hang on too long, either. My grand-dad was like that about driving. He was crowding 90 years old, running over stuff right and left, but couldn’t see that it was time to quit.
In matters of faith, there is never a quitting time, but there are times when people get involved in areas of responsibility that they are not suited for, and in those cases, the wise words of Kenny Rogers should be heeded: “You’ve got to know when to hold’em and know when to fold’em.”