Zen prescribes that you should do your best at whatever you do, but you should not feel sad when you fail to succeed.Het prentje: vier ervaren zentennissers, omstreeks 1910, via antiqueathlete.
Restrict your evaluation to your act, and refrain from allowing the evaluation of the act to become a judgment of yourself as a person. It is certainly possible to judge that a tennis stroke was hit badly without judging the hitter to be a bad person or even a bad tennis player. This separation of the evaluation of the act from evaluation of the actor is exceedingly valuable mental hygiene for everyone, at all times.
Julian L. Simon, Good Mood. The New Psychology of Overcoming Depression, Open Court, La Salle Ill., 1993.