Before you say TGIF, here’s some news: it’s Friday the 13th. Considered the unluckiest day of the year, the 13th only falls on a Friday twice during 2017 (the second one will be in October). In order for a month to have a Friday the 13th, the month must begin on a Sunday.

No one really knows why Friday the 13th is so feared. Some say that it’s origins come from the Bible, since Jesus was crucified on a Friday and there were 13 guests at the Last Supper.

The fear goes beyond superstition: people have actually developed a phobia of Friday the 13th, called paraskevidekatriaphobia. Millions of people across the U.S. will avoid their normal routines or even avoid getting out of bed because of this fear. Friday the 13th also inspired a huge movie franchise.