What is "principle of least astonishment"

n. (context software user interface design English) A principle that the design should match the user's experience, expectations, and mental models.

The principle of least astonishment (POLA), sometimes also referred to as Principle of Least Surprise, applies to user interface and software design, from the ergonomics standpoint. It is alternatively referred to as the law or rule of least astonishment, or of least surprise. The principle can be stated as "if a necessary feature has a high astonishment factor, it may be necessary to redesign the feature." In general engineering design contexts, the principle may be taken to mean that a component of a system should behave in a manner consistent with how users of that component are likely to expect it to behave, i.e., users should not be astonished at the way it behaves.