" Getting even was the basis of many primate semantic confusions, such as"expropriating the expropriators," "an absolute crime demands an absolute penalty," "they did it to me so I can do it to them," and, in general, the emotional mathematics of "one plus one equals zero" (1 + 1 = 0).

The primates were so dumb they didn't realize that one plus one equals two (1 + 1 = 2) and one murder plus one murder equals two murders, one crime plus one crime equals two crimes, etc. "

― Robert Anton Wilson , Schrödinger's Cat Trilogy