Friday the 13th facts (and superstitions) you likely did not know

Many people have araskavedekatriaphobia (also known as friggatriskaidekaphobia), or fear of Friday the 13th.

Here are 13 facts about Friday the 13th:

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It's not clear where the superstition originates. Some believe it stems from the Biblical Last Supper, in which the unlucky 13th guest, Judas, betrays Jesus.
Another Biblical belief is that Cain killed his brother, Abel, on Friday the 13th.
Friday the 13th can come in threes - all years will have at least one Friday the 13th and as many as three Friday the 13ths in any given calendar year.
More than 100 of the Knights Templar are also believed to have been tortured and later killed by King Philip IV of France on Friday, Oct. 13, 1307.
If you have triskaidekaphobia, or fear of the number 13, you likely also have araskavedekatriaphobia — fear of Friday the 13th. Dr. Donald Dossey, a folklore historian, estimates that 17 to 21 million people suffer from triskaidekaphobia.
Beloved rapper Tupac Shakur was killed on Friday, Sept. 13, 1996. Another notable Friday the 13th death was that of Julia Child in Aug. 2004.
Some numerologists believe the number 13 is considered unlucky because of its relation to the number 12. Numerologists consider 12 a "complete" number: 12 months in a year, 12 apostles, 12 tribes of Israel, 12 labors of Hercules, 12 gods of Olympus, 12 hours on a clock.
According to National Geographic, more than 80 percent of highrise buildings avoid having a 13th floor. Hospitals skip the 13th floor and many hotels skip having a room No. 13. Some airports even skip having a gate 13.
The "Friday the 13th" movie franchise is going strong, despite many people's fears. Since the first film premiered in 1980, the franchise's 12 films have grossed more than $380 million at the box office worldwide, according to Box Office Mojo.
Some symptoms of the phobia of the number 13 range from anxiety to all-out panic attacks. Many people will skip work on Friday the 13th.
The number 13 is considered lucky by some. For pagans, it represents the number of full moons in a year.
Historian and founder of the Stress Management Center and Phobia Institute in Asheville, North Carolina, Donald Dossey, told National Geographic, "It's been estimated that [U.S.] $800 or $900 million is lost in business on this day because people will not fly or do business they normally would do."
Mary Kate and Ashley Olsen were born on Friday the 13th in 1986. Other celebs include Steve Buscemi, Julia Louis-Dreyfus, Kate Walsh and director Alfred Hitchcock. Perhaps that explains his obsession with psychological thrillers?