Murphy's law
noun [ U ] humorous uk/ˌmɜː.fiz ˈlɔː/ us/ˌmɝː.fiz ˈlɑː/ (UK offensive also Sod's law)
墨菲法则（一种认为凡有可能出差错的事终将出差错的论断）
the principle that if it is possible for something to go wrong, it will go wrong
The bus is always late but today when I was late it came on time - that's Murphy's law! 那一路公共汽车总是晚点，可是今天我迟到了，它却准时来了——我想那一定是墨菲法则在起作用。