I guess there is the theory side talkiing here, and also the practical application side.....
As an injured, slow, blind, old, weak fart, I cannot ever beat someone who outruns every ball I hit, so I have to hit it better and better, until I beat myself.
Same me, young big hitter, I cannot match power and speed, so have to with better placement and smarter placements, until I beat myself hitting too close to the lines.
Against another 63 year old slow guy, I can hit 60% on my shots, and win most of them, so why try to play at 90%, and beat myself?
In tennis, as in life, you have to analyse, adapt, and perform the shots you need to win, and it's different for different opponent's and situations.