In 1990, Godwin got fed up with Nazi comparisons on bulletin boards, Usenet newsgroups, and the WELL discussion site. So prevalent had these comparisons become that Godwin began to wonder “how debates had ever occurred without having that handy rhetorical hammer.”He believed that most of these comparisons simply trivialized the Holocaust and the true horror of the Nazi regime and so consciously decided to build a “countermeme designed to make discussion participants see how they were and are acting as vectors to a particularly silly and offensive meme.” The result was Godwins Law in its original form:As an online discussion grows longer, the probability of a comparison involving Nazis or Hitler approaches one.

via No Nazi comparisons? Sounds like something Hitler would say!.