Do you have triskaidekaphobia* (fear of the number 13)? Ever wonder how Friday the 13th became such an unlucky day?
National Geographic provides a summary of the mythic and religious associations with the number 13.
For a more in-depth look at how this day got a bad reputation and how other superstitions started, check out these books:
Holiday folklore, phobias, and fun : mythical origins, scientific treatments, and superstitious "cures"
Dossey, Donald E.
The encyclopedia of superstitions
A treasury of American superstitions
Lys, Claudia de.
Why people believe weird things : pseudoscience, superstition, and other confusions of our time
*Triskaidekaphobia translates from Greek as tris (three), kai (and), deka (ten), phobia (fear).