Murphy's law

Murphy's law is an adage in Western culture that broadly states that if anything can go wrong, it will. "If there's more than one possible outcome of a job or task, and one of those outcomes will result in disaster or an undesirable consequence, then somebody will do it that way." It is most often cited as "Whatever can go wrong, will go wrong" (or, alternately, "Whatever can go wrong will go wrong, and at the worst possible time, in the worst possible way").