A few words of advice: If you ever find yourself backstage at a theater or attending a rehearsal, make sure not to whistle and, if you’re the last one to leave, don’t switch all the lights off. If the play happens to be Shakespeare’s Macbeth, remember to only refer to it as “the Scottish play”—the success of the production could depend on it.

Some of these superstitions originally made perfect sense. The first stagehands were thought to be sailors, hired for their knowledge of knots and ropes. As they did on a ship, the sailors would use coded whistles to communicate and—though many now believe such stories to be apocryphal—a careless whistle could cause chaos with the scene changes. Similarly, the single “ghost light” that is always left on somewhere in a theater, s...