Man has always had superstitions about numbers and about days. Some were supposed to be lucky; some, unlucky. Why the number 13 came to be considered unlucky no one really knows, though there are some theories about it. One explanation has to do with Scandinavian mythology. There were 12 demi Gods. According to this legend, Loki appeared, making the 13th. Since Loki was evil and cruel and caused human misfortunes, and since he was the 13th demigod, the number 13 came to be a sign of bad luck.