"If I were a plant, I would be a plastic plant. My doctor says I have a malformed public-duty gland and a natural deficiency in moral fibre," he muttered to himself, dejectedly. But wait—wrong book. Let us turn instead to the nature of design.
You approach a door. The handle is a vertical bar that stands out from the door surface. You grasp it and pull. The door refuses to open. You pull harder. Nothing. You look closely and see a small sign: PUSH.
The door has no handles. It is a flat plate. You push. The door opens. Why did the first door fail? Because the design gave a false clue. A vertical bar signals "pull." A flat plate signals "push." When the signal is wrong, the design is at fault, not the user.
— Excerpt adapted from The Design of Everyday Things by Don Norman.
The correct parts must be visible, and they must convey the correct message. If a function is hidden, it is hard to use.
Feedback is the return of information about the result of an action. Without it, one is left wondering if anything happened.
The perceived and actual properties of the thing, primarily those fundamental properties that determine just how the thing could possibly be used.
The relationship between two things, in this case between the controls and their movements and the results in the world.
Good design is actually a lot harder to notice than poor design, in part because good designs fit our needs so well that the design is invisible, serving us without drawing attention to itself. Bad design, on the other hand, screams out its inadequacies, making itself very noticeable indeed.