This is ubiquitous. Another variant: you think of a way to cheat; you assume your opponent is villainous and always cheats; so you assume your opponent was alre

This is ubiquitous. Another variant: you think of a way to cheat; you assume your opponent is villainous and always cheats; so you assume your opponent was already cheating in this specific way; so you cheat in this specific way "to even the playing field". As soon as you accept it as axiomatic that the other guy cheats you are liberated from the rules yourself out of fairness. And you are still the righteous hero! How dare the other guy be so villainous, and so cunning as to hide it! He forced you to do a dastardly thing! He's ruining X for everyone!