Designing a consistently usable User Interface

The goal of every UI designer is to design a user interface that is intuitive, simple, and easy to learn so that the user can effortlessly develop a mental model (understanding) of the product. This requires a consistency of usability throughout the entirety of the interface. Nothing may frustrate users more than suddenly discovering a confusing or poorly conceived section of an otherwise incredibly user-friendly UI. They may find themselves taking blame for their confusion, thinking that since the rest of the user interface was so easy, the solution to their current problem will be just as easy and it is some error on their part that is the obstacle.