History of Friday the 13th
There is no reliable evidence that Friday the 13th was considered to be especially inauspicious before the late nineteenth century, though both Friday and the number thirteen were separately identified as negative. Because of this, attempts to explain the superstition with reference to historical events are speculative.
One proposed origin relates to the Last Supper. Judas, the thirteenth guest, was instrumental in the Crucifixion of Jesus, which happened on a Friday.
Other theories offered in relation to Friday suggest that Eve offered the apple to Adam on a Friday or the slaying of Abel happened on a Friday (though the Bible does not identify the days of the week when these events occurred).
It is also sometimes claimed that the superstition derived from the massacre of the Knights Templar on Friday October 13, 1307. King Philip IV of France ordered the destruction of the Templars, after having claimed that they were engaged in heretical practices. Philip sent letters to his forces all over the country with instructions to open that morning. The orders were simple - seek out and arrest all known members of the Knights, slaughter those that resisted, and capture Jacques DeMolay, the last known Grand Master of the Knights Templar. (See also History of the Knights Templar)
However, no evidence is known to link the superstition to any specific events or suggest that there is any continuity from the Middle Ages to the present day.
Effects in people and cultures
"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 would normally do,"
Some people are so paralyzed by fear that they are simply unable to get out of bed when Friday the 13th rolls around. The Stress Management Center and Phobia Institute estimates that more than 17 million people are affected by a fear of this day.
A British Medical Journal study has shown that there is a significant increase in traffic related accidents on Friday the 13ths. Despite that representatives for both Delta and Continental Airlines say that their airlines don't suffer from any noticeable drop in travel on those Fridays.
The date is well-known in the motorcycle (biker) community: Since 1981, motorcycle enthusiasts and vendors gather every Friday the 13th in Port Dover, Ontario, Canada. This tradition started on November 13, 1981 by Chris Simons as a gathering of approximately 25 friends. The event has grown substantially, with an estimated 100,000 people attending in August 2004, as well as music bands, vendors, a bike show, etc.
In the Spanish-speaking world, it is Tuesday the 13th (as well as Tuesdays in general) that brings bad luc; a proverb runs En martes, ni te cases ni te embarques (on Tuesday, neither get married nor start a journey)
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taken from here.