The Design of Everyday Things

by Donald A. Norman

Two of the most important characteristics of good design are discoverability and understanding. Discoverability: Is it possible to even figure out what actions are possible and where and how to perform them? Understanding: What does it all mean? How is the product supposed to be used? What do all the different controls and settings mean?

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

Designers need to focus their attention on the cases where things go wrong, not just on when things work as planned.

Affordances exist even if they are not visible. For designers, their visibility is critical: visible affordances provide strong clues to the operations of things.

Perceived affordances help people figure out what actions are possible without the need for labels or instructions.

Affordances determine what actions are possible. Signifiers communicate where the action should take place.

Good design requires, among other things, good communication of the purpose, structure, and operation of the device to the people who use it.