There are a few theories as to why people say “break a leg” instead of “good luck.” One theory is that the phrase comes from Shakespeare. In Shakespeare’s time, it was considered bad luck to wish someone good luck before they went on stage. So, people would instead tell the actors to “break a leg,” meaning that they hoped the play would be successful.
Another theory is that the phrase comes from ancient Greece. In Greek theater, it was customary to sacrifice an animal before a play. So, when an actor was told to “break a leg,” it meant that they were being asked to make a sacrifice for the success of the play.
Whatever the origins of the phrase, it is now commonly used in theater and other performing arts as a way to wish someone good luck.