Answer:
A combination of other superstitions concerning Friday and the number 13, being further compounded by popular culture, myth and folklore made it unlucky.
Friday 13th is considered unlucky because of the following reasons:
- Friday has been seen as a day of ill omen by Christians because it is supposed to be the day on which Jesus was crucified. So when the thirteenth of the month coincides with Friday, it’s a particularly dismal omen.
- Some historians trace the Christian distrust of Fridays to the church's overall opposition to pagan religions. Friday is named after Frigg, the Norse goddess of love and sex. This strong female figure posed a threat to male-dominated Christianity. To fight her influence, the Christian church characterized her as a witch, vilifying the day named after her. This characterization may also have played a part in the fear of the number 13. It was said that Frigg would often join a coven of witches, normally a group of 12, bringing the total to 13.
- According to legend, in the 18th century, the British Navy commissioned a ship called the H.M.S. Friday, in order to quell the superstition. The navy selected the crew on a Friday, launched the ship on a Friday and even selected a man named James Friday as the ship's captain. Then, one Friday morning, the ship set off on its maiden voyage -- and disappeared forever.
- In Norse mythology, the beloved hero Balder was killed at a banquet by the malevolent god Loki, who crashed the party of twelve, bringing the group to 13
- On a Friday the 13th in 1306, King Philip of France burned the revered Knights Templar at the stake, marking the occasion as a day of evil.
- A similar Christian tradition holds that 13 is unholy because it signifies the gathering of 12 witches and the devil.
- The early Romans thought 13 was a sign of death and destruction.
- A properly constructed hangman's noose consists of 13 wraps above the noose.
- The number of steps leading to the gallows platform usually ended up being 13.
- Some people fear Friday the 13th because of misfortune they've experienced on that day in the past.
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