Friday the 13th Is an Unlucky Day
"The superstition that Friday the 13th specifically is a day prone to bad luck or misfortune."
Bad luck attached to the number 13 and to Fridays both have long, separate folklore histories, well before they were ever combined into a single unlucky date. Norse mythology tells of the trickster god Loki crashing a banquet of twelve gods as an uninvited thirteenth guest, setting off a chain of events that gets one of the other gods killed. Christian tradition points to the Last Supper, where Judas, whose betrayal led directly to the crucifixion the next day, a Friday, is remembered as the thirteenth person at the table. The specific combination of Friday and the 13th as one unlucky date, rather than two separate superstitions, seems to be a more modern invention, commonly linked to the 1907 American novel Friday, the Thirteenth, which helped cement the pairing in popular culture.