"And on a Friday fell all this mischance"

Not a red letter day?
I'm not sure you all remember quotes from the Canterbury Tales and if you do, perhaps make room in your brain for something else:

"And on a Friday fell all this mischance"...

I was looking at the Friday the 13th stuff online and figuring out the why and have concluded that other than Rossini, the composer, dying on Friday the 13th, the bad luck day just seems to be a combination of Friday being the week's unlucky day (which also might have some anti-Semitic overtones) and 13 being a bad number.
Woodcut from the Canterbury Tales 1473 

I grew up Lutheran, and numerology was a big part of the church's religious history. 12 was perfect and a lot of religion and common time keeping makes note of that (twelve months of the year, twelve hours of the clock, twelve gods of Olympus, twelve tribes of Israeltwelve Apostles of Jesusthe 12 successors of Muhammad in Shia Islam, twelve signs of the Zodiac).

Thirteen however seems to be the "odd man out"...one too many as it were.  Actually there is a myth that having 13 at dinner or around the dinner table is a sure sign that one will die.  That's comforting as our table  has good room for 6,  poor room for 12 and no room for 13....that person has to eat off a counter top.

So have a nice Friday the 13th....and Jason is just a movie character.