Mur ‧ phy’s law /ˌmɜːfiz ˈlɔː $ ˌmɜːrfiz ˈlɒː/ BrE AmE noun [uncountable] informal especially American English
[ Date: 1900-2000 ; Origin: Edward Murphy (born 1917), U.S. engineer who first thought of it ]
a tendency for bad things to happen whenever it is possible for them to do so – used humorously SYN sod’s law British English