MOST people who believe that Friday the 13th is an unlucky day fail to offer a reasonable explanation why. The superstition does have deep roots and the belief is widespread but, as freeracer notes, you don't have to be affected!
It is accepted that the fear of Friday the 13th stems from two separate fears -- the fear of the number 13 and the fear of Fridays. Both fears have deep roots in Western culture, most notably in Christian theology.
Thirteen is significant to Christians because it is the number of people who were present at the Last Supper (Jesus and his 12 apostles). Judas, the apostle who according to the Bible betrayed Jesus, was the 13th member of the party to arrive.
Christians have traditionally been wary of Fridays because Jesus was said to have been crucified on a Friday. Additionally, some theologians hold that Adam and Eve ate from the forbidden fruit on a Friday, and other say that the Great Flood began on a Friday.
Sailors were particularly superstitious. They often refused to sail out on a Friday. According to unverified legend, the British Navy commissioned a ship in the 1800s called H.M.S. Friday, in order to quell the superstition. The navy selected the crew on a Friday, launched the ship on a Friday and even selected a man named James Friday as the ship's captain. Then, one Friday morning, the ship set off on its maiden voyage... and disappeared forever. A similar story is the harrowing flight of Apollo 13.
The number 13 could also have been considered as something Pagan. The Pagan lunar calendar has 13 months and corresponds to the human menstrual cycle, connecting the number to femininity.
Some trace the infamy of the number 13 back to ancient Norse mythology, in which the hero Balder was killed at a banquet by the mischievous god Loki, who crashed the party of twelve, bringing the group to 13. This, as well as the story of the Last Supper, led to one of the most entrenched 13-related beliefs: You should never sit down to a meal in a group of 13.
Both Friday and the number 13 were once closely associated with capital punishment. In British tradition, Friday was the conventional day for public hangings, and there were supposedly 13 steps leading up to the noose.
Ultimately, the complex folklore of Friday the 13th doesn't have much to do with people's fears today. The fear has much more to do with personal experience. At a young age, people are taught that Friday the 13th is supposed to be unlucky. Dozens of horror movies play on this fear. The evidence isn't hard to come by, of course. If you get in a car wreck on one Friday the 13th, lose your wallet, or even spill your coffee, that day will probably stay with you. But of course, if one thinks about itt, bad things, big and small, happen all the time. If you're looking for bad luck on Friday the 13th, you'll probably find it.
- researched on google.com, including wikipedia.org and howthingswork.com, adpated by freeracer