Susan here, on Friday the 13th – the first Friday 13th of 2023 (the second will be in October). We all do a bit of a double-take on any Friday the 13th, but why? Some who are genuinely superstitious about it may have triskaidekaphobia, or fear of the number 13, while others may be so superstitious that they develop a fear of Friday the 13th in particular, called paraskevidekatriaphobia (from the Greek) or friggatriskaidekaphobia (from the Norse “frigg,” the root word of Friday).
What is it about this particular day, or the number 13? Let’s take a look.
Probably the earliest and certainly the most well-known cause of superstition around the number 13 is due to the attendance at the Last Supper of the 13th Apostle, Judas, who betrayed Jesus at the supper held on the 13th of Nisan, later called Maundy Thursday. From that developed an understandable superstition about 13 guests at a dinner table. . .
In Norse myth—not based in Christianity, so perhaps rising independently—there is a story of a feast of the gods in Valhalla when Loki, being the 13th and uninvited arrival, took offense and provoked one god to kill another, the god of light and joy--whose death brought darkness and destruction to the realm of the Norse gods.

In the fairytale realm, another party ended in disaster in the Brothers Grimm story of Briar-Rose, or Sleeping Beauty. The king and queen, celebrating at last the birth of a child, a beautiful baby daughter, host a dinner and invite fairies to bless her with gifts and protection. Having only twelve golden plates for the table, they declined to invite a thirteenth fairy—who arrived in a snit, cursing the child with the prediction that she would prick her finger on a needle and die at the age of 16.