Much of the tension in product development and interface design comes from trying to balance the obvious, the easy, and the possible. Figuring out which things go in which bucket is critical to fully understanding how to make something useful. Shouldn’t everything be obvious? Unless you’re making a product that just does one thing – like a paperclip, for example – everything won’t be obvious. You have to make tough calls about what needs to be obvious, what should be easy, and what should be possible. The more things something (a product, a feature, a screen,...