The problems which most perplex tennis players are not those deal- ing with the proper way to swing a racket. Books and professionals giving this information abound. Nor do most players complain excessively about physical limitations. The most common com- plaint of sportsmen ringing down the corridors of the ages is, “It’s not that I don’t know what to do, it’s that I don’t do what I know!”

W. Timothy Gallwey, The Inner Game of Tennis, London, 1975, p. 13