Michael Jordan stated "As strong as my legs are, it is my mind that has made me a champion." The statement was in reference to his will to win, confidence in his talents and the mental grit he often displayed playing through physically grueling situations, including sickness.
Two quotes that share the same common message that many great athletes have espoused as apart of their game plan for victory - you have to believe you can win. You have to believe you are the best. It will motivate you to your best.