An American scientist once visited the offices of the great Nobel-prize-winning physicist, Niels Bohr, in Copenhagen. He was amazed to find that over Bohr's desk was a horseshoe, securely mailed to the wall, with the open end up in the approved manner (so it would catch the good luck and not let it spill out). The American said with a nervous laugh, "Surely you don't believe the horseshoe will bring you good luck, do you, Professor Bohr?" 

"As a scientist," Bohr chuckled, "I believe no such thing, my good friend. Not at all. I am scarcely likely to believe in such foolish nonsense. However, I am told that a horseshoe will bring you good luck whether you believe in it or not."