Wrote George Gamow in "Thirty Years that Shook Physics":
Above the front door of his country cottage in Tisvilde he nailed a horseshoe, which is proverbially instrumental in bringign luck. Seeing it, a visitor exclaimed: "Being as a great scientist as you are, do you really believe that a horseshoe above the entrance to a home brings luck?" "No," answered Bohr, "I certainly do not believe in this superstition. But you know," he added with a smile, "they say that it does bring luck even if you don't believe in it!"