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What's behind the Friday the 13th superstition?

Do you suffer from friggatriskaidekaphobia? That is, a morbid, irrational fear of Friday the 13th?

If so, you're not the only one - apparently, President Franklin D. Roosevelt also suffered from it, avoiding travel on the 13th day of any month, and never hosting 13 guests at a meal.

So where does the superstition around Friday the 13th come from? Well, there are a number of theories as to where this relatively modern superstition comes from.

First of all, 12 is a very common number in the West. "There are 12 hours, 12 months and in Christianity 12 apostles and this is a divine number. Add one more and it brings in a certain element of chaos," said Ulo Valk, professor of comparative folklore at the University of Tartu in Estonia, to the Associated Press.

According to historians, on Friday, October 13th, 1307, King Philip IV of France ordered the arrests of thousands of the Knights Templar on accusations of heresy, resulting in the executions of more than a hundred of the Crusades warriors. The theory of this as the superstition's origin appeared in Dan Brown's novel "The Da Vinci Code."

The association may also be biblical.

The Last Supper's 13th guest was Judas, who betrayed Jesus. His crucifixion was the next day, a Friday.

In reality, the Friday the 13th superstition is a fairly modern phenomenon. As Volk pointed out, "less than 100 years ago, the number 13 did not have this sinister meaning."

But its manifestations can be seen in a number of areas: High-rise buildings and hotels often skip the 13th floor, and hospitals often do not have a Room 13.

Some airports and airlines skip a gate 13 or row 13, respectively.

According to the Stress Management Center and Phobia Institute in Asheville, N.C., the fear of freaky Friday can be costly too; businesses and airlines lose up to $900 million a year because of it.

Some other Friday the 13th trivia: It's horror movie master Alfred Hitchcock's birthday.

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