How is Friday the 13th considered "Bad Luck"?

One theory suggested by OJ Ivey states that Jesus dies on a Friday and there were 13 people at the last supper.

On the other hand, another theory by author Charles Panati, one of the leading authorities on the subject of “Origins” maintains that the superstition can be traced back to ancient myth:

The actual origin of the superstition, though, appears also to be a tale in Norse mythology. Friday is named for Frigga, the free-spirited goddess of love and fertility. When Norse and Germanic tribes converted to Christianity, Frigga was banished in shame to a mountaintop and labeled a witch. It was believed that every Friday, the spiteful goddess convened a meeting with eleven other witches, plus the devil — a gathering of thirteen — and plotted ill turns of fate for the coming week. For many centuries in Scandinavia, Friday was known as "Witches' Sabbath."[11]

Another theory about the origin of the superstition traces the event to the arrest of the legendary Knights Templar. According to one expert:

The Knights Templar were a monastic military order founded in Jerusalem in 1118 C.E., whose mission was to protect Christian pilgrims during the Crusades. Over the next two centuries, the Knights Templar became extraordinarily powerful and wealthy. Threatened by that power and eager to acquire their wealth, King Philip secretly ordered the mass arrest of all the Knights Templar in France on Friday, October 13, 1307 - Friday the 13th.[4]

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