Mario's cartridge: Tennis and the Feral Prodigy (p. 176)
How promising you are as a Student of the Game is a function of what you can pay attention to without running away. Nets and fences can be mirrors. And between the nets and fences, opponents are also mirrors. This is why the whole thing is scary. This is why all opponents are scary and weaker opponents are especially scary. See yourself in your opponents. They will bring you to understand the Game.
Context
The cartridge's closing credo converts the court into a hall of mirrors: nets, fences, and opponents all reflect the player back at himself, and the Game becomes managed fear of one's own reflection. The book's mirror-optics at their most benign — the same instrument the A.F.R. will point the other way (163) and AA will haul out in front of newcomers (166).