"What appears to have happened in the 19th century, maybe the early 20th century is that these two unlucky things - the number 13 and Friday - were put together," Assistant Professor of History at Minot State, Mark Singer said.
He said the myth of Friday's being unlucky stems from Christianity, as Christ was said to be crucified on a Friday, therefore making it bad luck.
As for the number 13 - he said in some of the earliest cultures in Mesopotamia, the basis used for numbers was 12.
He explained that's why a circle is measured as 360 degrees, it's a multiple of 12 -- same for why we have 24 hours in a day.
Thus, 13 is considered unlucky simply because it's one more than 12.
He said our culture again goes back to Christianity and the very old tradition that claims it unlucky to have 13 people sitting at the table in reference to the Last Supper.
As for the modern-day superstition, he said it's really just a matter of making sense of outright bad luck.
"I think that a lot of the way that we make sense of the world is we look for external things that affect the world. We're seeing two things that could possibly have affect," Singer said.
"Friday and 13 and we put them together. Maybe because if we know that this is an unlucky day, then we're not surprised by anything that happens, it's comforting to us."
Christian or not, the superstition dates back centuries in the U.S.
Singer said in the late 19th century there was an elite dining club called the 13 Club.
As a way of countering superstition, people gathered on the 13th and would have 13 people eat together and then brag in the ads that no one died.
Some peope even consider the date to be especially lucky.