The number 13 is supposed to be unlucky because there were 13 people at the last Supper, and Judas was the thirteenth guest. Another theory says that it’s unlucky because there were 12 Scandinavian demigods until Loki, the evil one, made 13. Whatever the original cause of belief, many people genuinely fear the 13th. Friday, too is supposed to be unlucky. This was the day when Christ died, and the day when Adam and Eva ate the forbidden fruit. So when Friday and 13 are put together, quite a few superstitious people feel that day is unlucky.
Why is Friday thirteenth considered unlucky?