Innovation begins with understanding the key elements. Metal, wood or glass are not key elements of a door to an innovator. A way to get in, a way to keep others out – these are key elements. Begin with these, and soon you’re imagining new ways to make a door. You could design a door that is opened by your voice (nice when your hands are full), or one that shuts and locks itself when anyone else approaches. Think of the key elements in things.