The "Friday the 13th" legend—the widespread Western superstition that this date brings bad luck—doesn't have a single, definitive origin. Instead, it combines older separate beliefs about the unluckiness of Fridays and the number 13, which merged relatively recently into the specific fear of their combination.
The Last Supper...
Why 13 Is Considered Unlucky
The number 13 has long been seen as ominous in many cultures, often because it disrupts the "completeness" of 12 (e.g., 12 months, 12 zodiac signs, 12 apostles, 12 gods in various pantheons).
Why Its Considered " Unlucky"?
In Christian tradition, the most cited link is the Last Supper, where Jesus dined with his 12 apostles (making 13 total). Judas (the 13th) betrayed Jesus, and the crucifixion followed the next day (a Friday, known as Good Friday).
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In Norse mythology, a famous tale describes 12 gods feasting in Valhalla when Loki (the trickster) crashes as the uninvited 13th guest. He tricks the blind god Höðr into killing the beloved Balder with mistletoe, leading to chaos and death—reinforcing 13 as a harbinger of misfortune.