>This observation applies only to amateur tennis. In professional tennis it’s just the opposite: 80% of the rallies are won rather than lost, as unforced errors are infrequent. This is true in chess as well, as high-level players don’t blunder, and thus it really is that litany of other skills that results in high standings.

I think this means at a high level, you're already not blundering. So you need to actually do something MORE in order to win. You need to force your oponent to lose, and not just play "OK" and wait for them to make a mistake.