 The fear of Friday the 13th
Since phobias concerns pple's mental health, I guess this could be under the "health" section.
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What do people fear most? At the top of the list is death, the fear of which is necrophobia. Second, apparently, is the fear of failure, which is called kakorrhaphiophobia. There is of course a story of how fears developed, like fear for the number 13. The fear of Friday the 13th is called paraskavedekatriaphobia.
In pagan times Friday was the luckiest day of the week because it was ruled by the planet Venus, the symbol of love and fortune. In fact, Friday is named in honour of Freya, goddess of Love. But for Christians, Friday has not been a good day. Adam and Eve is said to have eaten the forbidden fruit on a Friday and died on a Friday. Jesus was crucified on a Friday.
For centuries sailors refused to set sail on a Friday. It is told that when the reluctance of seamen to set sail on a Friday had reached such proportions that it interfered with naval operations, the British Admiralty decided to prove once and for all that it is a fallacy. They laid the keel of a new vessel on a Friday, named her H.M.S. Friday, and launched her on a Friday. On her first voyage, setting sail on a Friday, she was commanded by Captain James Friday. She left the harbour and nothing has since been heard of her or her crew. The identical story has also found its place in American lore.
The fear for traveling on a Friday continued until the early 20th century where in Europe bus and train travel was lowest on a Friday. But before you say "Thank Goodness, it's Friday!" consider that today, FBI statistics show, most robberies take place on a Friday.
The number 13
It is believed that the fear for the number 13 stems from primitive man being unable to count past 12. Numbers beyond 12 do now have an individual and independent name but are a combination of the first 12 numbers. With 12 being the end of the line, 13 was moving into unknown territory.
In Norse mythology the 13th number led to the death of Baldur, the beloved of the gods. When the 12 gods gathered for a banquet in Valhalla, Loki gatecrashed the party, increasing the number to 13, which led to the death of Baldur. It also happens that in Tarot cards, 13 is called "Death."
The baker's dozen
The "unlucky 13" is the reason why the thirteen loaves that bakers once supplied were never called by the number, but described as "a baker's dozen." The thirteenth loaf was regarded as a special bribe for the devil not to spoil the sale or the bread.
But 13 is not unlucky for all. The Mayas worshipped the 13 gods of the upper world. The Aztecs climbed 13 steps to their sacred places. Buddhists paid homage to 13 Buddhas. In Jewish faith, God revealed Himself by 13 attributes of bountiful mercy (Exodus 34: 6-7). The orthodox Jewish prayer book hold the Thirteen Principles of Faith. Jewish boys celebrate their Bar Mitzvah at age 13.
The number 13 in Greek is triskaideka and the fear of the number 13 is called triskaidekaphobia.  Open me up. See the Springs and Wires that Make the Clockwork Girl Spin. | 
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