Book Summary: "The Design of Everyday Things" by Dan Norman

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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?

Industrial design: The professional service of creating and developing concepts and specifications that optimize the function, value, and appearance of products and systems for the mutual benefit of both user and manufacturer.

Interaction design: The focus is upon how people interact with technology. The goal is to enhance people’s understanding of what can be done, what is happening, and what has just occurred. Interaction design draws upon principles of psychology, design, art, and emotion to ensure a positive, enjoyable experience.

Experience design: The practice of designing products, processes, services, events, and environments with a focus placed on the quality and enjoyment of the total experience.

We have to accept human behavior the way it is, not the way we would wish it to be.

The solution is human-centered design (HCD), an approach that puts human needs, capabilities, and behavior first, then de- signs to accommodate those needs, capabilities, and ways of behaving. Good design starts with an understanding of psychology and technology. Good design requires good communication, especially from machine to person, indicating what actions are possible, what is happening, and what is about to happen.

Experience is critical, for it determines how fondly people re- member their interactions. Was the overall experience positive, or was it frustrating and confusing?

When we interact with a product, we need to figure out how to work it. This means discovering what it does, how it works, and what operations are possible: discoverability.

The term affordance refers to the relationship between a physical object and a person. An affordance is a relationship between the properties of an object and the capabilities of the agent that determine just how the object could possibly be used.

If an affordance or anti-affordance cannot be perceived, some means of signaling its presence is required: I call this property a signifier.

Perceived affordances help people figure out what actions are possible without the need for labels or instructions. I call the signaling component of affordances signifiers.

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

Summary: • Affordances are the possible interactions between people and the environment. Some affordances are perceivable, others are not. • Perceived affordances often act as signifiers, but they can be ambiguous. • Signifiers signal things, in particular what actions are possible and how they should be done. Signifiers must be perceivable, else they fail to function.

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

A device is easy to use when the set of possible actions is visi- ble, when the controls and displays exploit natural mappings. The principles are simple but rarely incorporated into design. Good design takes care, planning, thought, and an understanding of how people behave.

Feedback has to be planned. All actions need to be confirmed, but in a manner that is unobtrusive. Feedback must also be prior- itized, so that unimportant information is presented in an unob- trusive fashion, but important signals are presented in a way that does capture attention.

A conceptual model is an explanation, usually highly simplified, of how something works. It doesn’t have to be complete or even accurate as long as it is useful.

I call the combined information available to us the system image. If it is incomplete or contradictory, there will be trouble.

Good conceptual models are the key to understandable, enjoy- able products: good communication is the key to good conceptual models.

The same technology that simplifies life by providing more functions in each device also complicates life by making the device harder to learn, harder to use. This is the paradox of technology and the challenge for the designer.


When people use something, they face two gulfs: the Gulf of Execution, where they try to figure out how it operates, and the Gulf of Evaluation, where they try to figure out what happened. The role of the designer is to help people bridge the two gulfs.

The Gulf of Evaluation reflects the amount of effort that the person mustmake to interpret the physical state of the device and to determine how well the expectations and intentions have been met.

There are two parts to an action: executing the action and then evaluating the results: doing and interpreting. Both execution and evaluation require understanding: how the item works and what results it produces. Both execution and evaluation can affect our emotional state.

Seven stages of actions:

  1. Goal (form the goal)
  2. Plan (the action)
  3. Specify (an action sequence)
  4. Perform (the action sequence)
  5. Perceive (the state of the world)
  6. Interpret (the perception)
  7. Compare (the outcome with the goal)

A root cause analysis: asking “Why?” until the ultimate, fundamental cause of the activity is reached.

The most basic level of processing is called visceral. This is some- times referred to as “the lizard brain.” The visceral system allows us to respond quickly and subconsciously, without conscious awareness or control.

For designers, the visceral response is about immediate per- ception: the pleasantness of a mellow, harmonious sound or the jarring, irritating scratch of fingernails on a rough surface. Here is where the style matters: appearances, whether sound or sight, touch or smell, drive the visceral response.

The behavioral level is the home of learned skills, triggered by sit- uations that match the appropriate patterns. Actions and analyses at this level are largely subconscious. Even though we are usually aware of our actions, we are often unaware of the details.

Feedback provides reassurance, even when it indicates a negative result. A lack of feedback creates a feeling of lack of con- trol, which can be unsettling. Feedback is critical to managing ex- pectations, and good design provides this. Feedback—knowledge of results—is how expectations are resolved and is critical to learn- ing and the development of skilled behavior.

The reflective level is the home of conscious cognition. As a conse- quence, this is where deep understanding develops, where reason- ing and conscious decision-making take place.

All three levels of processing work together to determine a person’s cognitive and emotional state. High-level reflective cognition can trigger lower-level emotions. Lower-level emotions can trigger higher-level reflective cognition.

Conceptual models are a form of story, resulting from our predis- position to find explanations. These models are essential in helping us understand our experiences, predict the outcome of our actions, and handle unexpected occurrences.

If designers and researchers do not sometimes fail, it is a sign that they are not trying hard enough—they are not think- ing the great creative thoughts that will provide breakthroughs in how we do things.

Вesigners should take special pains to make errors as cost-free as possible.

They can’t communicate and under- stand the same way we do. This means that their designers have a special obligation to ensure that the behavior of machines is un- derstandable to the people who interact with them.

The hard and necessary part of design is to make things work well even when things do not go as planned.

The seven-stage model of the action cycle can be a valuable de- sign tool, for it provides a basic checklist of questions to ask. In general, each stage of action requires its own special design strate- gies and, in turn, provides its own opportunity for disaster.

  1. What do I want to accomplish?
  2. What are the alternative action sequences?
  3. What actions can I do now?
  4. How do I do it?
  5. What happened?
  6. What does it mean?
  7. Is it okay? Have I accomplished my goal?

The information that helps answer questions of execution (doing) is feedforward. The information that aids in understanding what has happened is feedback.

The insights from the seven stages of action lead us to seven fun- damental principles of design:

  1. Discoverability. It is possible to determine what actions are possible and the current state of the device.
  2. Feedback. There is full and continuous information about the results of actions and the current state of the product or service. After an action has been executed, it is easy to determine the new state.
  3. Conceptual model. The design projects all the information needed to create a good conceptual model of the system, leading to under- standing and a feeling of control. The conceptual model enhances both discoverability and evaluation of results.
  4. Affordances. The proper affordances exist to make the desired actions possible.
  5. Signifiers. Effective use of signifiers ensures discoverability and that the feedback is well communicated and intelligible.
  6. Mappings. The relationship between controls and their actions follows the principles of good mapping, enhanced as much as possible through spatial layout and temporal contiguity.
  7. Constraints. Providing physical, logical, semantic, and cultural con- straints guides actions and eases interpretation.


Precise behavior can emerge from imprecise knowledge for four reasons:

  1. Knowledge is both in the head and in the world.
  2. Great precision is not required.
  3. Natural constraints exist in the world.
  4. Knowledge of cultural constraints and conventions exists in the head.

Short-term or working memory (STM) retains the most recent ex- periences or material that is currently being thought about. It is the memory of the just present. Information is retained automatically and retrieved without effort; but the amount of information that can be retained this way is severely limited.

Long-term memory (LTM) is memory for the past. As a rule, it takes time for information to get into LTM and time and effort to get it out again.

There are two different aspects to a reminder: the signal and the message. Just as in doing an action we can distinguish between knowing what can be done and knowing how to do it, in reminding we must distinguish between the signal—knowing that something is to be remembered, and the message—remembering the infor- mation itself.

Tradeoffs Between Knowledge in the World and in the Head

Here are three levels of mapping, arranged in decreasing effectiveness as memory aids: • 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.


Physical limitations constrain possible operations. The value of physical constraints is that they rely upon properties of the physical world for their operation; no special training is necessary.

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.

Affordances, signifiers, mappings, and constraints can simplify our encounters with everyday objects. Failure to properly deploy these cues leads to problems.

In many cases it is better to have switches that control activities: activity-centered control.

Forcing functions are a form of physical constraint: situations in which the actions are constrained so that failure at one stage pre- vents the next step from happening.

An interlock forces operations to take place in proper sequence. A lock-in keeps an operation active, preventing someone from prematurely stopping it. A lockout prevents someone from entering a space that is dangerous, or prevents an event from occurring.

The clever designer has to minimize the nuisance value while retaining the safety feature of the forcing function that guards against the occasional tragedy.


When people err, change the system so that type of error will be reduced or eliminated. When complete elimination is not possible, redesign to reduce the impact.

A slip occurs when a person intends to do one action and ends up doing something else. With a slip, the action performed is not the same as the action that was intended. There are two major classes of slips: action-based and memory-lapse. In action-based slips, the wrong action is performed. In lapses, memory fails, so the intended action is not done or its results not evaluated. Action-based slips and memory lapses can be further classified according to their causes.

A mistake occurs when the wrong goal is established or the wrong plan is formed. From that point on, even if the actions are executed properly they are part of the error, because the actions themselves are inappropriate—they are part of the wrong plan. Mistakes have three major classes: rule-based, knowledge-based, and memory-lapse. In a rule-based mistake, the person has appropriately diagnosed the situation, but then decided upon an erroneous course of action: the wrong rule is being followed. In a knowledge-based mistake, the problem is misdiagnosed because of erroneous or incomplete knowledge. Memory-lapse mistakes take place when there is forgetting at the stages of goals, plans, or evaluation.

Social pressures show up continually. They are usually difficult to document because most people and organizations are reluctant to admit these factors, so even if they are discovered in the process of the accident investigation, the results are often kept hidden from public scrutiny.

Checklists are powerful tools, proven to increase the accuracy of behavior and to reduce error, particularly slips and memory lapses. They are especially important in situations with multiple, complex requirements, and even more so where there are interruptions.

We need to make it easier to report errors, for the goal is not to punish, but to determine how it occurred and change things so that it will not happen again.

Many systems compound the problem by making it easy to err but difficult or impossible to discover error or to recover from it. It should not be possible for one simple error to cause widespread damage. Here is what should be done:

  • Understand the causes of error and design to minimize those causes.
  • Do sensibility checks. Does the action pass the “commonsense” test?
  • Make it possible to reverse actions—to “undo” them—or make it harder to do what cannot be reversed.
  • Make it easier for people to discover the errors that do occur, and make them easier to correct.
  • Don’t treat the action as an error; rather, try to help the person complete the action properly. Think of the action as an approximation to what is desired.

Prevention often involves adding specific constraints to actions. In the physical world, this can be done through clever use of shape and size.

Perhaps the most powerful tool to minimize the impact of errors is the Undo command in modern electronic systems, reversing the operations performed by the previous command, wherever pos- sible.

he request for confirmation seems like an irritant rather than an essential safety check because the person tends to focus upon the action rather than the object that is being acted upon. A bet- ter check would be a prominent display of both the action to be taken and the object, perhaps with the choice of “cancel” or “do it.”

  • Make the item being acted upon more prominent.
  • Make the operation reversible.

Slips most frequently occur when the conscious mind is distracted, either by some other event or simply because the action being per- formed is so well learned that it can be done automatically, without conscious attention.

Many slips can be minimized by ensuring that the actions and their controls are as dissimilar as possible, or at least, as physically far apart as possible.

What we call “human error” is often simply a human action that is inappropriate for the needs of technology. As a result, it flags a deficit in our technology. It should not be thought of as error. We should eliminate the concept of error: instead, we should realize that people can use assistance in translating their goals and plans into the appropriate form for technology.


Engineers and businesspeople are trained to solve problems. De- signers are trained to discover the real problems. A brilliant solu- tion to the wrong problem can be worse than no solution at all: solve the correct problem.

Two of the powerful tools of design thinking are human-centered design and the double-diamond diverge-converge model of design.

Human-centered design (HCD) is the process of ensuring that people’s needs are met, that the resulting product is understandable and usable, that it accomplishes the desired tasks, and that the experience of use is positive and enjoyable.

The Design Council divided the design process into four stages: “discover” and “define”—for the divergence and convergence phases of finding the right problem, and “develop” and “deliver”—for the divergence and convergence phases of finding the right solution.

There are four different activities in the human-centered design process:

  1. Observation
  2. Idea generation (ideation)
  3. Prototyping
  4. Testing These four activities are iterated; that is, they are repeated over and over, with each cycle yielding more insights and getting closer to the desired solution.

Design wants to know what people really need and how they actually will use the product or service under consideration. Marketing wants to know what people will buy, which includes learning how they make their purchasing decisions.

Idea generation rules:

  • Generate numerous ideas.
  • Be creative without regard for constraints.
  • Question everything.

Prototyping during the problem specification phase is done mainly to ensure that the problem is well understood. If the target popu- lation is already using something related to the new product, that can be considered a prototype. During the problem solution phase of design, then real prototypes of the proposed solution are invoked.

Gather a small group of people who correspond as closely as pos- sible to the target population—those for whom the product is in- tended. Have them use the prototypes as nearly as possible to the way they would actually use them.

Like prototyping, testing is done in the problem specification phase to ensure that the problem is well understood, then done again in the problem solution phase to ensure that the new design meets the needs and abilities of those who will use it.

The hardest part of design is getting the requirements right, which means ensuring that the right problem is being solved, as well as that the solution is appropriate. Requirements made in the abstract are invariably wrong. Requirements produced by asking people what they need are invariably wrong. Requirements are de- veloped by watching people in their natural environment.

The design practices described by the double-diamond and the human-centered design process are the ideal. Even though the ideal can seldom be met in practice, it is always good to aim for the ideal, but to be realistic about the time and budgetary challenges. These can be overcome, but only if they are recognized and designed into the process. Multidisciplinary teams allow for enhanced communi- cation and collaboration, often saving both time and money.

Designers need to understand their customers, and in many cases, the customer is the person who purchases the product, not the person who actually uses it. It is just as important to study those who do the purchasing as it is to study those who use it.

Fixed solutions will invariably fail with some people; flexible solutions at least offer a chance for those with dif- ferent needs.

Standards can take so long to be established that by the time they do come into wide practice, they can be irrelevant. Nonetheless, standards are necessary. They simplify our lives and make it possible for different brands of equipment to work together in harmony.


The design of technology to fit human needs and capabilities is determined by the psychology of people. Yes, technologies may change, but people stay the same.

Creeping featurism is the tendency to add to the number of fea- tures of a product, often extending the number beyond all reason. There is no way that a product can remain usable and understand- able by the time it has all of those special-purpose features that have been added in over time.

Good design requires stepping back from competitive pressures and ensuring that the entire product be consistent, coherent, and understandable.

Ideas that are too early often fail, even if eventually others introduce theme successfully.

Most design evolves through incremental innovation by means of continual testing and refinement. In the ideal case, the design is tested, problem areas are discovered and modified, and then the product is continually retested and remodified.

Incremental innovation starts with existing products and makes them better. Radical innovation starts fresh, often driven by new technologies that make possible new capabilities.

Reliance on technology is a benefit to humanity. With technol- ogy, the brain gets neither better nor worse. Instead, it is the task that changes. Human plus machine is more powerful than either human or machine alone.

With massive change, a number of fundamental principles stay the same. Human beings have always been social beings. Social interaction and the ability to keep in touch with people across the world, across time, will stay with us.