Be A Competitor
Nothing can compensate for the lack of will to perform when the situation demands that desire!
Only you can provide this will. No one clue can help at the moment of truth. The penalty for the lack of will is usually defeat. (Either mental and/or physical)
"Quitting" is any time the athlete gives up hope of doing his/her best. The difference between a winner and a loser is often the effort to try. The winner tries and therefore regardless of results is a winner. There is no failure like ceasing to try.
Propers training is an extremely important part of being a winner. It does not guarntee success, but it certainly increases the possibilities.
Providing the "potential" is there, mental factors such as courage, will-to-win, subconscious desire for victory, capacity to suffer, fearless determination, frustration, tolerance, and good old intestinal fortitude (otherswise known as "guts" or "gumption") must be combines with proper training to transform potential into reality and give any assurance of success. These mental factors can only come from within the athlete.
You must work at developing your inner motivation. This is a learned skill!
From Motivation and Coaching Psychology by Wilt and Bosen.