Design of Everyday Things: Knowing What to Do

This chapter begins with an experiment involving Legos, in which a 13 piece motorcycle has constructed with no prior information or guidance purely based on the set physical, semantic, and cultural constraints applied to it. Physical constraints limit possibilities - a square peg cannot be placed in a round hole. No special training is required to understand physical constraints because they are governed by the world, however, their effectiveness is determined by the ease with which they can be determined and interpreted. Semantic constraints rely on the meaning of the situation - in this case, there is only one sensible position for the driver. Cultural constraints rely on accepted conventions - signs should be visible, screws are tightened clockwise. In this case, the "Police" sign on the motorcycle should be placed right-side-up and in a visible location and the clear yellow brick is obviously a headlight, as is the convention. Logical contraints applied to the construction of the motorcycle include the imperative that all blocks be used with no gaps in the final product. Natural mappings work by providing logical constraints.
Next the author discusses several examples of poor design. He begins by re-addressing the door situation presented in chapter 1. Then, he moves on to discussing switches, which frequently lack a logical mapping and grouping. These discussions are conducted in the context of mapping and constraint principles discussed in previous chapters.
The principle of visibility states that relevant parts should be made visibile and the feedback principle states that actions should have an immediate and obvious effect. Visibility allows users to infer how an object is manipulated and what these manipulations can be expected to produce. Feedback allows users to learn through trial-and-error and reduce misattributions of causality and misconceptions. Feedback can be given visually or audibly. In fact, most sounds made by devices aren't made out of necessity, they are made to inform the user that an event has occurred (such as the shutter sound made by a digital camera).