Best mapping: Controls are mounted directly on the item to be controlled. • Second-best mapping: Controls are as close as possible to the object to be controlled. • Third-best mapping: Controls are arranged in the same spatial configuration as the objects to be controlled.

Constraints are powerful clues, limiting the set of possible actions. The thoughtful use of constraints in design lets people readily determine the proper course of action, even in a novel situation.

Design is concerned with how things work, how they are controlled, and the nature of the interaction between people and technology.

Designers need to focus their attention on the cases where things go wrong, not just on when things work as planned. Actually, this is where the most satisfaction can arise: when something goes wrong but the machine highlights the problems, then the person understands the issue, takes the proper actions, and the problem is solved.

Mapping is a technical term, borrowed from mathematics, meaning the relationship between the elements of two sets of things.

The partnership of technology and people makes us smarter, stronger, and better able to live in the modern world.

Semantics is the study of meaning. Semantic constraints are those that rely upon the meaning of the situation to control the set of possible actions.

So we must design our machines on the assumption that people will make errors.

Suppose I try to use an everyday thing, but I can’t. Who is at fault: me or the thing? We are apt to blame ourselves, especially if others are able to use it. Suppose the fault really lies in the device, so that lots of people have the same problems. Because everyone perceives the fault to be his or her own, nobody wants to admit to having trouble.