An American scientist once visited the offices of the great Nobel Prize-winning physicist, Neils Bohr, in Copenhagen, and was amazed to find a horseshoe was nailed to the wall over his desk.

The American said with a nervous laugh, "Surely you don't believe that horseshoe will bring you good luck, do you, Professor Bohr?"

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!  How can one argue with such logic?"