Friday the 13th has long been associated with bad luck, but how did the day get such a scary reputation?  One explanation is that Friday and the number 13 both have violent historical connections to Christianity. It was on a Friday that Jesus was crucified, and ever since, the day has been associated with a "general ill omen," Michael Bailey, a history professor at Iowa State University who specializes in the origins of superstitions, tells USA TODAY Network. Read more at the link in our bio.