Murphy's law
According to David J. Hand, emeritus professor of mathematics and senior research investigator at Imperial College London, Sod's law is a more extreme version of Murphy's law. While Murphy's law says that anything that can go wrong, will go wrong (eventually), Sod's law requires that it "always" goes wrong with the worst possible outcome. Hand suggests that belief in Sod's law is a combination of the law of truly large numbers and the psychological effect of the law of selection. The former says we should expect things to go wrong now and then, and the latter says we remember the exceptional events where something went wrong, but the great number of mundane events where nothing exceptional happened are forgotten.