Don Norman — Principles of Interaction

How people understand and operate things. Use to diagnose why a control is unintuitive, not just that it is.

• Affordances & Signifiers: What an object can do (affordance) vs the perceptible cue telling the user it can (signifier). Most "discoverability" bugs are missing signifiers.
• Mapping: Spatial / logical correspondence between controls and their effects (stove knobs → burners). Natural mapping removes a learning step.
• Feedback: Every action gets a visible, immediate response. Silence reads as failure.
• Constraints: Physical, logical, semantic, and cultural limits that prevent error before it happens.
• Conceptual Model: The user's mental picture must match how the system actually behaves. Mismatch = confusion that no copy can fully patch.
• Gulf of Execution / Gulf of Evaluation: The gap between intention → action, and between system-state → understanding. Design must close both: make actions obvious (execution) and results legible (evaluation).

How to apply

• Confusing control? Ask which is missing: affordance, signifier, mapping, or feedback.
• Bridge the Gulf of Execution with clear signifiers; bridge the Gulf of Evaluation with clear feedback and status.
• When users hold a wrong mental model, fix the model (structure, naming, behavior) before adding help text.