Ruby slippers
The ruby slippers are the shoes worn by Dorothy in The Wizard of Oz which give her the power of returning home any time she wishes. She acquired the shoes after her house fell on the Wicked Witch of the East, killing her and liberating the Munchkins. (In the original novel, they were silver slippers, but this was changed for the movie to take advantage of the movie being in colour.)
Dorothy knew that the slippers were powerful, but was unaware of their powers. It was only at the end of the film that she learned the formula: click your heels together three times, and repeat "There's no place like home."
Software engineers sometimes refer to the 'ruby slippers effect' whereby a program provides a valuable feature overlooked by its user.
