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, which were actually silver in the original Baum book, after her house fell on the Wicked Witch of the East, killing her and liberating the Munchkins.

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.