You must have complete determination. The worst opponent you can come across is one whose aim has become an obsession. For instance, if a man has decided that he is going to bite off your nose no matter what happens to him in the process, the chances are he will succeed in doing it. He may be severely beaten up, too, but that will not stop him from carrying out his objective. That is the real fighter.

p. 161 - The Warrior Within : The Philosophies of Bruce Lee (1996)