The belief that bad luck comes in threes is a classic example. A couple things go wrong, and believers may start to look for the next bit of bad luck. A lost shoe might be forgotten one day, but seen as the third in a series of bad breaks the next.
According to folklore, breaking a mirror is a surefire way to doom yourself to seven years of bad luck. The superstition seems to arise from the belief that mirrors don’t just reflect your image; they hold bits of your soul. That belief led people in the old days of the American South to cover mirrors in a house when someone died, lest their soul be trapped inside.
