Friday the 13th is said to be unlucky because it combines a historically unlucky day and unlucky number.
The No. 13 has long gotten the human race riled up -- back to ancient times. It's even led to a condition called triskaidekaphobia, fear of the number 13.
That fear for 13 has led to some strange decisions and unusual behavior in the past. Here are 13 examples.
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No room in the inn
Hospitals and hotels regularly have no room number 13.
On the street
Many cities don't have a 13th Street or a 13th Avenue. This city tempted fate.
Blame your parents
If you have 13 letters in your name, you're said to have the devil's luck. Like, this guy (Charles Manson).
Checking in
Many airports skip the 13th gate.
Aisle omission
Airplanes have no 13th aisle.
Numero...?
Italians omit the number 13 from their national lottery.
Unlucky height
More than 80% of high rises lack a 13th floor
One solution
On streets in Florence, Italy, the house between number 12 and 14 is addressed as 12 and a half.
Hangman's noose
Traditionally in hangings, there are 13 knots in the noose and 13 steps leading up to the moment of death.
Dinner luck
French President Nicolas Sarkozy may know that in France, socialites called quatorziens (fourteeners) make themselves available as 14th guests to keep a dinner party from an unlucky fate.
Space travel
Many say the No. 13 pointed to the ill-fated mission to the moon, Apollo 13.
It's in the cards
Tarot Card number 13 is the Death Card, depicting the Grim Reaper.
Ancient ties
Some say that the Babylonian Code of Hammurabi (circa 1780 B.C.E.) is to blame for the No. 13 woes since the 13th law is omitted.
First Posted: 11/16/10 11:19 AM ET Updated: 05/25/11 03:40 PM ET