Paraskevidekatriaphobia - the fear of Friday the 13th.
While there is no mention of Friday the 13th until the writings of the 19th Century, some posit that the fear is rooted in the religious. According to National Geographic:
"The trepidation surrounding Friday the 13th is rooted in religious beliefs surrounding the 13th guest at the Last Supper—Judas, the apostle said to have betrayed Jesus—and the crucifixion of Jesus on a Friday, which was known as hangman's day and was already a source of anxiety..."
There are numerological implications surrounding the Number 13 as well. According to numerology, the number 13 has the strange misfortune of being placed behind the number 12, considered to be a complete number (there are 12 signs of the Zodiac, 12 months in the year, 12 tribes of Israel, 12 Apostles of Jesus, etc.). The number 13, therefore, is seen as 'less than' or 'slightly beyond completeness', adding to its mystery.
There are those who believe that if you can pronounce the word paraskevidekatriaphobia, you will be cured of the fear. While there is much speculation as to where this mysterious "holiday" began, there is no doubt there will be many of us steering clear of black cats, ladders, and many other superstitious symbols associated with 'bad luck' today.
What superstitions or fears do you have?