The Design of Everyday Things
TRY TO OPEN THE DOOR
Core Principles
Good design is about how things work, not just how they look. Start with these four essentials.
Affordance
The properties of an object suggest how it can be used. A button looks pressable.
Signifiers
Signals that indicate where and how to act. Without them, users guess.
Mapping
The relationship between controls and effects. Natural mapping feels obvious.
Feedback
The system must tell users what happened. Without it, people feel lost.
Gulfs of Execution & Evaluation
Users face two gaps: how to act (execution) and what happened (evaluation). Design must bridge both.
User
Has goals and intentions
System
Has state and mechanics
Case: Using a Projector
Gulf of Execution
"I want to project my laptop, but I don't know which button to press."
- ✗30 buttons with cryptic symbols.
- ✓Design: one large button labeled "Input".
Gulf of Evaluation
"I pressed the button, but the screen is still black. Is it broken or warming up?"
- ✗No lights or sounds.
- ✓Design: power light blinks, screen shows "Warming up...".
Mental Models
Users build a model of how a product works. When it diverges from the design model, errors follow.
How designers think it works
What users actually see
How users think it works
The Thermostat Fallacy
✗User's Wrong Model (Valve Theory)
"If I set the AC to 60°F, the room cools faster."
✓Actual Model (Switch Theory)
AC is simply on or off. Lowering the target only keeps it on longer.
Design lesson: if users keep failing, their model and your design model differ. Change the system image to teach the right model.
Constraints
Constraints limit possible actions and reduce errors. Use physical, logical, semantic, and cultural constraints.
Physical Constraints
Shape and fit prevent misuse. E.g., this plug only fits this socket.
CLICK SHAPES TO PLACE (FORCING FUNCTION)
Logical Constraints
Logic blocks invalid actions. E.g., submit stays disabled until required fields are filled.
Logical Constraint: Action blocked until conditions met.
Errors
Humans err. Design should forgive. Norman distinguishes slips (right goal, wrong action) and mistakes (wrong goal).
Slips
Goal is right, action deviates—often during skilled behavior with low attention.
- [EXAMPLE]Adding milk to coffee, then putting the milk back but leaving the coffee on the counter.
- [DESIGN FIX]Design fix: provide undo; add distinct cues.
Mistakes
The goal itself is wrong—often from a flawed mental model.
- [EXAMPLE]Misreading system state, making a bad plan, and executing it.
- [DESIGN FIX]Design fix: better feedback; clearer system state; confirmations.
THE DESIGN OF EVERYDAY THINGS
Don't let bad design ruin your life
If you've ever felt stupid pushing a pull door or fighting a remote, remember: it's not you, it's the design. This book rewires how you see the world.
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