How is it, exactly, that Friday the 13th got unlucky? Some say it relates to the number of diners at the Last Supper of Jesus, or, more simply, death. The Egyptians believed in many stages of spiritual existence, the thirteenth happening after the body died. Some theorise that priests of patriarchal religions purposely vilified it because it represented femininity: 13 revered in ancient goddess-worshipping cultures because it corresponded to the number of menstrual cycles in a year. Some people are so afraid of it that they even have a phobia all their own: Paraskevidekatriaphobia.