When we talk about being ‘consistent’ we mean ensuring that the core experience of a certain action or event remains the same each time a user performs that action or experiences that event.

A well constructed operating system UI for example will have consistent placement of the close button on a window. This is an action which you don’t want to have to think much about, it gets ingrained in your muscle memory and any friction faced while performing this action is sure to be felt in frustration rather than delight.

This is actually a good example, as, in the two leading systems (MacOS and Windows) have the close button in opposite corners of the window, this doesn’t matter to either set of users, until you switch between operating systems and then it can become a source of frustration.

Consistency helps the user know what to expect. It’s not flashy, it’s not exciting, but it’s something which works and is very easy to implement.