Suppose you are playing a man who unfortunately has Alzheimers. He cannot remember the score from point to point and even if you put up the score on the net post, he forgets to look at it.
Is it OK to cheat and always make the score favorable to yourself? After all, he cannot reliably argue with you even if he suspects you are cheating. Since he cannot prove it because his memory is medically certified as unreliable, it is OK to cheat, correct?