Many physical objects are becoming icons, or symbolic representations of what they do. Much like the floppy disk save icon, the physical interfaces of many products today reference older technologies that are now obsolete. What can drive the metaphors that are used in today's interfaces? As digital technology replaces the mechanisms physical interfaces were once based on, how can we create interfaces that help people understand how to interact with the functions they control? If the way something actually works is so complex or counter-intuitive that it won't make sense to the average user, should the interface attempt to present a simplified metaphor? And if there is no older physical metaphor to fall back on, what principles can guide the creation of new interaction metaphors?