A theory states that the longer an Internet discussion goes on, the probability of a Hitler or Nazi reference approaches 100%
It's known as Godwin’s law. In 1990, during the early days of the Internet, Mike Godwin observed that, given enough time, in any online discussion, someone would invariably criticize something someone else said by comparing it to something Hitler or the Nazis would have said.
The rule doesn’t claim to say that the reference in question is appropriate or inappropriate, only that the longer a discussion continues, the likelihood that Hitler or the Nazis will be brought up increases.
Because of the frequency at which this happens, Godwin has argued that overuse of these references should be avoided because it lessens the impact of the comparison.
When Godwin first formed the idea, it referred specifically to discussions on Usenet. Today, he says it applies to any threaded online discussion, but the meaning behind it stays the same. Godwin wanted people who throw out Nazi references to think harder about the Holocaust instead of just tossing the names around.
Media Matters today suggests that Godwin’s Law is no longer limited to internet forums and the like because of the frequency that Hitler and the Nazis are referenced on national television in the news and other media outlets.