Why is Friday the 13th Unlucky?

Source

At dawn on Friday the 13th of October, 1307, orders from King Philip were opened all across France accusing the Knights Templar of heresy. Agents of the King, promptly arrested the members of the order to be imprisoned, tortured and once admitting to their sacrilegious offenses put to death. Some novels have presented this as the origin of the superstition of Friday the 13th being the most unlucky of days; most famously, Dan Brown's The Da Vinci Code.

But is there any truth to this origin story? There are two parts to this Friday the 13th story; the Friday part and the 13th part; both of which have separately being considered as unlucky throughout history.

We’ll start with a devils dozen, 13. In many cultures, 12 has been a good number: There are 12 months in a year, 12 hours in a day, 12 signs of the zodiac, 12 labors of Hercules, 12 successors of Muhammad in Shia Islam, 12 tribes of Israel, 12 disciples of Jesus and the list goes on. So perhaps 13 just has the unfortunate distinction of being one too many for a perfect 12. However there could be more to this, 13 guests at a dinner party has been considered unlucky in western culture; some say this stems from Norse mythology. Legend has it that 12 gods were invited to a feast in Valhalla. Loki, the god of mischief, arrived uninvited and tricked Hod, the blind god of darkness, to attack Baldur, the god of joy and gladness, with mistletoe, which just so happened to be the only thing deadly to Baldur. However, we have to be careful with Norse mythology, many of the writings we have about the Vikings were written by Christian poets and artists centuries after the Vikings were gone, and they may have taken some inspiration from a biblical story. And that story is also a candidate for the origin of 13 being an unlucky number, and suggests that the superstition may have arisen in the Middle Ages from the story of Jesus' last supper and crucifixion, where the thirteenth guest to sit at the table is said to have been Judas who later betrayed Jesus leading to his crucifixion. As was standard in the Roman Empire, Jesus is said to have been crucified on a Friday? And this is one possible origin for Friday bringing bad luck.

But that’s not the only Friday that has a bad reputation in the bible. By tradition, it was on a day yet to be named Friday when Eve tempted Adam with the forbidden fruit, it was a Friday when the Great Flood began, it was a Friday when God tongue-tied the builders of the Tower of Babel, it was a Friday when the Temple of Solomon was destroyed. It seems Friday in Christianity, unless it is Good Friday, is destined to be bad. Furthermore, the name of the day, Friday, is derived from the Old English goddess Frigg, the pagan goddess of sex and fertility. To the Romans it was the day of Venus, and to these pagans it was a day of worship and even a fine day to become wed given the goddesses association with love. But all that … love … isn’t something the new Church could stand for, so by the Middle Ages Friday had become known as the "Witches' Sabbath”. And I note, a witches' coven is "properly" comprised of exactly 13 members.

The Last Suffer (Source)

So what exactly is the origin of Friday the 13th? As you may have come to guess by my ramblings, the exact origins are not entirely clear, and these are not the only theories out there - links for further reading in the description. However, it was not until the early 20th century that regular references to Friday the 13th as a day of bad luck become common in the press; and it seems more likely that the unlucky 13 and the unlucky Friday was an inevitable match made in heaven, or is that hell?

Today, however, most people dismiss these as silly superstitions. And with good reason as according to the Dutch Centre for Insurance Statistics there are on average 7,800 traffic accidents each Friday in the Netherlands; but on a Friday the 13th there are, on average, 300 less; probably because some avoid driving and others take extra care. So perhaps what we should take from all this is that regardless of the day, a little extra care might make the day, whatever the date, a bit luckier.

The reference:
http://urbanlegends.about.com/cs/historical/a/friday_the_13th.htm
http://www.snopes.com/luck/friday13.asp
http://www.infoplease.com/spot/friday13th.html
http://mentalfloss.com/article/52696/why-friday-13th-considered-unlucky
http://uk.reuters.com/article/us-luck-idUKL1268660720080613