Concepts

The ideas and definitions the rest of the handbook builds on. Each concept page gives you a working definition, the evidence behind it, where it shows up in the strategies and Tools, Techniques, and Practices (TTPs), and a For engineers and agents section that translates the idea into implementation and review terms—so you can use the vocabulary precisely instead of by vibe. Several pages include Mermaid diagrams for the core process (states, awareness, habit cues, trust movements, agency audit).

Read Customer Discovery alongside these pages: concepts name the mechanisms; discovery names whose experience you are designing.

The handbook’s own frame:

• Feeling North Star: The one emotion a surface should reliably produce—named before any pattern is chosen.
• Tools, Techniques, and Practices (TTPs): The modular unit of this handbook, and how strategies compose them.

Product-design vocabulary:

• Surfaces, Flows, and States: The units of design work—and the five states every surface has whether designed or not.
• Friction: The budget of taps, waits, reading, and doubt every surface spends—and where to place it deliberately.
• Mental Models and Affordances: The user’s private theory of how your product works, and the cues that shape it.

The science:

• Emotional Design: Norman’s visceral, behavioural, and reflective levels—the frame beneath every card.
• Peak–End Rule: Why the most intense moment and the ending decide what users remember.
• Aesthetic–Usability Effect: Why craft changes perceived ease—and how it can hide real friction.
• Jobs-to-be-Done (JTBD): The progress users hire your product to make.
• Habit Formation: How context-cued routines form, and where return design ends and compulsion begins.

The boundaries:

• Calibrated Trust: Earning the right amount of confidence—neither blind reliance nor dead-weight doubt.
• User Agency: The line between persuasion and manipulation, and why this handbook refuses dark patterns.
• Investment and Continuity: Honouring what users build—without sunk-cost traps or hostage data.
• Social Transmission: Share artefacts, invite people, bridge contacts—growth with consent at every hop.