The Principle of Least Astonishment, in shorthand, encompasses what we, as designers, must achieve to ensure consistency in our designs. Consistency is a fundamental design principle for usable user interfaces. But the thing that astonishes me is that it’s actually necessary to explain this principle. Surprise implies the unexpected. Of course, users want the response to a given action to be what they expect; otherwise, they would have done something else. In user interactions, the unexpected is pretty much the same as the unwanted. Surprise usually implies something bad rather than something positive—unless users already have such dismally low expectations of their software that they might think, Wow! It worked. I’m so astonished.