In the states it's quite common to number the floors of a building by avoiding the number 13. I think this is pure madness. 10, 11, 12, 14, 15... All of that because of a fantasy book where people had supper and they happen to be 13 at the table. Edit: Here's an example: https://en.wikipedia.org/wiki/13_(number)#/media/File:Many_b...
Well, this fantasy book led to much more crazy behaviors. Beside this, the same is true for many other fantasy things like money or ethics.