Friday 13th considered unlucky by some who believe bad things occur on 13th day of the month if a Friday. This superstition has evolved from many sources however, the most predominant is Jesus Christ’s “last supper” where thirteen people were present one betraying Christ leading to His crucifixion and death on Good Friday.
The number considered “unnatural” while number twelve is natural as in twelve months of a year, twelve hours in a day, and Christ had twelve apostles.
Hollywood has benefitted from this superstition turning out many horror films related to this day. Evil portrayed as happening during unnatural times, places, or situations particularly during the thirteenth day on a Friday.