Break a leg

A well-known expression in the world of theatre, wishing an actor good luck, especially on opening night. It goes hand in hand with the theatrical superstition that to wish an actor good luck will invoke the very opposite. There are many theories as to the origin, ranging from breaking a leg meaning to bow when taking applause, to the assassin John Wilkes Booth breaking a leg when he jumped down from the balcony after killing Abraham Lincoln in 1865. The other theories are too tedious to detail; all of them suffering from the etymological weakness in that break a leg is a relatively modern expression, not dating from before 1930 and not appearing in print before 1948. The John Wilkes Booth story and others mostly take place in the 19th century. Idioms do not suddenly spring up close to one hundred years after their alleged origins. The most plausible explanation is that break a leg is simply based on the theatrical superstition that to wish someone good luck invariably invokes the opposite and, therefore, in wishing them to break a leg, good fortune as opposed to bad will follow.