Similar to how Four Is Death and 108 is significant, the number thirteen is often considered an unlucky number in the western world. There is some debate over the source of fear towards the number thirteen, though the writer Nathaniel Lachenmeyer has argued that the original 'unlucky thirteen' superstition was the 19th century belief that if thirteen people sat at a dinner table one would die before the end of the year. (Presumably he hadn't read the Greek myth using the trope.) Certainly it was established by the early 20th century when the word triskaidekaphobia was coined to describe an irrational fear of the number thirteen, a fear which has become so prevailent that many buildings in America will not have a 13th floor. If it is not particularly subtle it's the writers beating you over