Godwin’s Law is an adage formulated by American attorney and author Mike Godwin in 1990. The law states:
As an online discussion grows longer, the probability of a comparison involving Nazis or Hitler approaches one.
The rule does not make any statement whether any particular reference or comparison to Hitler or the Nazis might be appropriate, but only asserts that one arising is increasingly probable. It is precisely because such a comparison or reference may sometimes be appropriate, Godwin has argued that overuse […] should be avoided, because it robs the valid comparisons of their impact.
As an ex-regular of Wikipedia’s Talk:Main_Page, this humorous law is permanently etched into my psyche.
(Mike Godwin was the first staff counsel of the EFF, and is currently general counsel for the Wikimedia Foundation.)