Some explanations from alltimelists.com...
*some contributing factors to the avoidance of the 13th which are both historical as well as biblical. For example, the number 12 is considered as a whole in numerology - the twelve tribes of Israel, the 12 apostles of Jesus and then the 12 successors of Muhammad in Shia Islam. Anything that is over is considered unwhole by numerologists.
*Another theory is mentioned by the author Dan Brown in his book about the crusaders and the Knights Templar. On Friday the 13th, 1307 hundreds of Knights Templar were arrested in Paris and throughout Europe. On October 13, 1307, France’s King Philip IV ordered the arrest of the Knight Templar for speculative reasons and many were murdered throughout Europe. Another reason, bound in blood, to avoid and fear Friday the 13th.
*Much paranoia for this day actually started in the 18th century. Henry Sutherland Edwards wrote in the 1869 biography of Gioachino Rossini, that: “He was surrounded with friends to his last day. He considered (the number) 13 to be unlucky until his last day and he also passed away on Friday the 13th.”
*Later, a novel published in 1907 titled Friday, the Thirteen by Thomas W., popularized the idea of this day. It used the superstition to wreak havoc throughout American culture.
In other words, it's a bunch of hooey. Fear not!
