Why Friday the 13th is Unlucky

Thothenki wants to share this article from MentalFloss that says “According to the Oxford University Press Dictionary of Superstitions, the first reference to Friday the 13th itself wasn’t until 1913. (So despite actually occurring on Friday, October 13, 1307, the popular notion that the Friday the 13th stigma comes from the date on which the famed order of the Knights Templar were wiped out by King Philip of France is just a coincidence.)

So why do skyscrapers skip the 13th floor, and other such superstitions persist?  This issue is examined in Why is Friday the 13th Considered Unlucky? at  Mental Floss.