Another fundamental principle – that things with the same function appear and behave in the same way – underpins the way in which we make sense of the world, including the products with which we interact. Consistency allows us to identify patterns and give them meaning, which in turn enables us to make sense of our experiences, to predict what might come next and to decide what choices to make in order to pursue our goals.
The same goes for interactive products: if the menu items on a website were organised differently on every page, the website would be rather difficult to use, as the user would have to search afresh on every page they visited. On the other hand, if a menu item linked to a different page each time the user followed it, the website would be impossible to use, as the user would have no way of knowing where they might end up every time they followed a link. Therefore, it is not enough for the elements of an interface to be perceivable: they need to be designed and organised with consistency, and interacting with them needs to yield consistent outcomes.