Interface elements like buttons, touchpoints and screens must do two important things beyond pure functionality.
First, they must give the user not just control but agency – that is, the controllable elements must be meaningful. Manipulating them must create a directed experience rather than just a succession of operations.
Second, controls must integrate with the content and avoid distracting the user from the experience. A good UI is unobtrusive; a great UI is never even noticed by the user –function blends seamlessly into form.