Design of Everyday Things - Norman, Don [106]
The same arguments apply to the relationship of system output to expectations. A critical part of an action is the evaluation of its effects. This requires timely feedback of the results. The feedback must provide information that matches the user’s intentions and must be in a form that is easy to understand. Many systems omit the relevant visible outcomes of actions; even when information about the system state is provided, it may not be easy to interpret. The easiest way to make things understandable is to use graphics or pictures. Modern systems (especially computer systems) are quite capable of this, but the need seems not to have been recognized by designers.
EXPLOIT THE POWER OF CONSTRAINTS, BOTH NATURAL AND ARTIFICIAL
Use constraints so that the user feels as if there is only one possible thing to do—the right thing, of course. In chapter 4 I used the example of the Lego toy motorcycle, which could be correctly put together by people who had never before seen it. Actually, the toy is not simple. It was carefully designed. It exploits a variety of constraints. It is a good example of the power of natural mappings and constraints, constraints that reduce the number of alternative actions at each step to at most a few.
DESIGN FOR ERROR
Assume that any error that can be made will be made. Plan for it. Think of each action by the user as an attempt to step in the right direction; an error is simply an action that is incompletely or improperly specified. Think of the action as part of a natural, constructive dialog between user and system. Try to support, not fight, the user’s responses. Allow the user to recover from errors, to know what was done and what happened, and to reverse any unwanted outcome. Make it easy to reverse operations; make it hard to do irreversible actions. Design explorable systems. Exploit forcing functions.
WHEN ALL ELSE FAILS, STANDARDIZE
When something can’t be designed without arbitrary mappings and difficulties, there is one last route: standardize. Standardize the actions, outcomes, layout, displays. Make related actions work in the same way. Standardize the system, the problem; create an international standard. The nice thing about standardization is that no matter how arbitrary the standardized mechanism, it has to be learned only once. People can learn it and use it effectively. This is true of typewriter keyboards, traffic signs and signals, units of measurement, and calendars. When followed consistently, standardization works well.
There are difficulties. It may be hard to obtain an agreement. And timing is crucial: it is important to standardize as soon as possible—to save everyone trouble—but late enough to take into account advanced technologies and procedures. The shortcomings of early standardization are often more than made up for by the increase in ease of use.3
Users have to be trained to the standards. The very conditions that require standardization require training, sometimes extensive training (that is OK: it takes months to learn the alphabet, or to type, or to drive a car). Remember, standardization is essential only when all the necessary information cannot be placed in the world or when natural mappings cannot be exploited. The role of training and practice is to make the mappings and required actions more available to the user, overcoming any shortcomings in the design, minimizing the need for planning and problem solving.
7.3 The Backward Clock. (Drawing by Eileen Conway.)
Take the everyday clock. It’s standardized. Consider how much trouble you would have telling time with a backward