When it comes to bad luck, there are few superstitions as pervasive in Western culture as that of Friday the 13th. Like crossing paths with a black cat and breaking a mirror, the notion of a day that can bring misfortune is deeply embedded -- even if believers can't quite explain why.
There's even a name to describe the irrational dread of the date: paraskevidekatriaphobia -- a specialized form of triskaidekaphobia, a fear of the number 13.
While Friday the 13th may feel like a rare phenomenon, our Gregorian calendar means that the 13th of any month is slightly more likely to fall on a Friday than any other day of the week. It is not, however, a universal superstition: In Greece and Spanish-speaking countries, it is Tuesday the 13th that is considered a day of bad luck, while in Italy, it is Friday the 17th that is met with fear.
