Paraskevidekatriaphobia is a “blind, unreasoning fear” of Friday the 13th, according to psychotherapist Donald Dossey in Ashville, N.C., who coined the word. Dossey tells his patients that when they learn to pronounce the name of their phobia they can consider themselves cured. It happens three times in 2015. Every year has at least one Friday the 13th, but there are never more than three. Paraskevidekatriaphobia is not to be confused with triskadekaphobia, which is the fear of the number 13.

Superstitions about Friday the 13th may have their roots in Christian mythology. Friday was considered the most unlucky day of the week: the day when Christ was crucified, the day when Adam ate the apple, the day Noah’s devastating flood began and the day Cain slew Abel. There were 13 people at the Last Supper, with Judas the first to get up and leave, and the first to die. It used to be considered unlucky to have a dinner party for 13 guests, as it was thought the first to leave would be the first to die.

Some say the fears refer to the pope’s betrayal of the Knights Templar on Friday, Oct. 13, 1307. Other theories include the number 13 being one number off from twelve, which is associated with completeness, such as the number of successors of Mohammed, the number of Tribes of Israel, the number of members of the Greek Pantheon, or even the number of hours on the clock or months of the year. Many skyscrapers have no 13th floor.

Friday the 13th causes such fear in some that they change their daily routine, staying home from work, or even staying in bed all day. The Stress Management Center and Phobia Institute in North Carolina says that 17 to 21 million Americans fear Friday the 13th, a phobia which gained popularity in the 20th century. The institute estimates that fear of this day costs the business world approximately $900 million.