Why Friday the 13th is linked to bad luck

The superstition around Friday the 13th draws on dark stories linked to both the number 13 and the day of the week, DR reports.

The number 13 has been associated with superstition since around 4,500 BC, says Caroline Nyvang, a tradition researcher at the Royal Danish Library. In ancient Mesopotamia, now known as Iraq, mathematicians noticed that 13 stood apart from the usual pattern, she says. The number later appeared as an ominous symbol in myths, stories and traditions.

Examples include Judas, described as the 13th disciple, and a Norse myth in which 13 gods sat at a table in Valhalla when Loki killed Balder. In the story of Sleeping Beauty, 12 of 13 fairies were invited to a feast, and the uninvited 13th fairy cursed the princess to sleep for 100 years.

Christian tradition also links Friday with misfortune because Jesus was crucified on a Friday, Nyvang says. But the combination of Friday and the number 13 only became widely established as an ominous date in the 1980s, with the American horror film Friday the 13th.

The superstition may also affect behaviour. Some airlines leave out row 13 on their planes, and insurance companies say there are slightly fewer accidents than usual on Friday the 13th. Nyvang says people may be a little more attentive in traffic that day. The date falls between one and three times a year.