Norse god Loki from 17th century Icelandic manuscript.
For sufferers of triskaidekaphobia ~ dread of the numeral 13 ~ last Friday was the 2010’s most unlucky day. But it was the only Friday the 13th for the entire year, while 2009 had nine of them, the highest number of Friday the 13ths possible on the Gregorian calendar.
National Geographic News explores the topic in an article quoting from the book Holiday Folklore, Phobias and Fun by folklore historian Donald Dossey. In his book, Dossey explores both the origins of the unlucky sentiments regarding the number 13 and of Fridays.
According to National Geographic News:
Dossey traces the fear of the number 13 ~ aka, triskaidekaphobia ~ to a Norse myth about 12 gods having a dinner party at Valhalla, Norse mythology's heaven. In walked the uninvited 13th guest, the mischievous god Loki. Once there, Loki arranged for Hoder, the blind god of darkness, to shoot Balder the Beautiful, the god of joy and gladness, with a mistletoe-tipped arrow. "Balder died, and the whole Earth got dark. The whole Earth mourned. It was a bad, unlucky day," Dossey said.
There is also a biblical reference to the unlucky number 13. Judas, the apostle said to have betrayed Jesus, was the 13th guest to the Last Supper.
As for Friday, it's well known among Christians as the day Jesus was crucified. Some biblical scholars believe Eve tempted Adam with the forbidden fruit on Friday. Perhaps most significant is a belief that Abel was slain by his brother Cain on Friday the 13th.
Meanwhile, in ancient Rome, witches reportedly gathered in groups of 12. The 13th was believed to be the devil.
Some people are so paralyzed by Friday the 13th superstitions that they refuse to fly, buy a house, or act on a hot stock tip, the article states. "It's been estimated that $800 or $900 million is lost in business on this day because people will not fly or do business they would normally do," said Dossey.