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The general consensus is that the phrase originated hundreds of years ago. Theater folk were suspicious and superstitious types. Because their work as actors was to "practice the art of lying," they thought that if they wished a fellow actor good luck, the opposite would happen. Consequently, we say the reverse. The phrase "break a leg" is rumored to have begun because someone did just that after being wished good luck. Some have suggested that the practice came from "the evil eye," an eastern European idea that cautioned never to tempt fate by wishing for good luck.