Friday is the day that Jesus was crucified. Friday has traditionally been a "bad-luck" day by superstitious people because of this. I don't know about the number 13. I AM religious but I am NOT superstitious. I read this someplace once: A British ship company once tried to prove it was superstitious nonsense. They built a ship called "Friday." They began building it on a Friday, completed it on a Friday, and launched it on a Friday. It sank on its first voyage!