Friday the 13th, a day associated with bad luck, has various origins and superstitions surrounding it. One belief connects it to the Last Supper, where there were 13 individuals present, including Judas who betrayed Jesus. Another theory links it to the arrest of the Knights Templar on Friday, October 13, 1307. The number 13 is often seen as unlucky due to its disruptive nature compared to the harmony of the number 12.