It's Friday the 13th! This date has been associated with bad luck for centuries. The fear of the number 13 has been given a scientific name: “triskaidekaphobia”; and on analogy to this the fear of Friday the 13th is called “paraskevidekatriaphobia”; and while it may seem like an outdated concept to fear the day, the superstition still lives. According to some estimations, the world loses $700 to $800 million in revenue on Friday the 13th because people do not want to conduct business on this day. And it's not just that, 80 percent of the high rise buildings reportedly skip the 13th floor and many airports and hospitals skip gate 13 and room 13, respectively.
Several theories have been proposed about the origin of the Friday the 13th superstition. The superstition surrounding this day may have arisen in the Middle Ages, “originating from the story of Jesus' last supper and crucifixion” in which there were 13 individuals present in the Upper Room on the 13th of Nisan Maundy Thursday, the night before his death on Good Friday. While there is evidence of both Friday and the number 13 being considered unlucky, there is no record of the two items being referred to as especially unlucky in conjunction before the 19th century.
A suggested origin of the superstition—Friday, 13 October 1307, the date Philip IV of France arrested hundreds of the Knights Templar—may not have been put together until the 20th century. It is mentioned in the 1955 Maurice Druon historical novel The Iron King.
Also in numerology the number twelve is considered the number of divine organizational arrangement or chronological completeness, as reflected in the twelve months of the year, twelve hours of the clock day, twelve gods of Olympus, twelve tribes of Israel, twelve Apostles of Jesus, the twelve successors of Muhammad in Shia Islam, twelve signs of the Zodiac, the 12 years of the Buddhist cycle, etc., whereas the number thirteen was considered irregular, transgressing this completeness.