Principle of least astonishment

The principle of least astonishment (POLA), aka principle of least surprise (alternatively a law or rule),[1][2] applies to user interface and software design.[3] It proposes that a component of a system should behave in a way that most users will expect it to behave. The behavior should not astonish or surprise users. The following is a formal statement of the principle: "If a necessary feature has a high astonishment factor, it may be necessary to redesign the feature."[4]

The term has been in use in relation to computer use since at least the 1970s.[5] Although first formalized in the field of computer technology, the principle can be applied broadly in other fields. For example, in writing, a cross-reference to another part of the work or a hyperlink should be phrased in a way that accurately tells the reader what to expect. In a book about fishing for bass, "For recipes on how to cook your catch, see chapter 4" should not lead the reader to a chapter about bass fishing seasons in various locations.