design-everyday-things

Analyze the two gulfs: execution (can users figure out what to do?) and evaluation (do they understand what happened?). Check discoverability through affordances, signifiers, constraints, mappings, and feedback, then walk the seven stages of action to find where users get stuck.

Affordances define what actions are possible between an object and a user, while signifiers communicate where and how to perform those actions. A button affords clicking; its color, label, and hover state are signifiers showing you to click it.

Use constraints to make wrong actions impossible: input validation, disabled states for invalid options, and forced sequences. Add undo for destructive actions, sensible defaults, and error messages that explain what went wrong and how to fix it without blaming the user.

Use this framework for foundational diagnosis of why interactions fail, such as confusing controls, poor feedback, or mismatched mental models. For heuristic-based usability scoring, the skill itself points to ux-heuristics, and for iOS patterns it points to ios-hig-design.

Norman's core insight is that there is no human error, only bad design. When the system image fails to communicate a correct conceptual model, users form wrong mental models and blame themselves. The fix is redesigning signifiers, feedback, and mappings, not retraining users.