Every game is composed of two parts, an outer game and an inner game. The outer game is played against an external opponent to overcome external obstacles, and to reach an external goal. Mastaring this game is the subject of many books offering instructions: on how to swing a racket, club or bat, and how to position arms, legs or torso to achieve the best results. But for some reason most of us find these instructions easier to remember than to execute.
"The Inner Game of Tennis"
W. Timothy Gallwey