When I was in high school (now I'm looking for time to write a post about it 🙂), in the grading journal, I was number 13. Not a single professor ever called me for answering by choise: "Let's go out on the board, under number XY".
For me, the number 13 is not a bad number.
People hold superstitions and a lot of the time they're unfounded although what a person believes will be their reality I guess...it's also easy for people to blame anything else except themselves for the bad things that occur in their lives.
A men finds the reason for his failure in a black cat, a disabled person, a shape of a cloud in the sky... Just so he doesn't look at himself in the mirror and think about what he can do to not be "malicious".