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Framework · The Hook Model · Hooked

The Hook Model

A four-step loop that product teams use to design habits: a trigger prompts an action, the action earns a reward that varies, and the user makes a small investment that sets up the next trigger. Many passes can move users from outside prompts to self-started use. The author calls it a practical tool, not a complete theory.

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Plain label: four-step habit loopAlso known as: Hooked, Nir Eyal, trigger action variable reward investment, habit loop, hook cycle

The four steps

  1. Trigger. Something prompts the behavior. External triggers carry the next step in the environment (a button, a message, an icon) and come in four types: paid, earned, relationship and owned. Internal triggers live in memory, as a link between a recurring feeling or routine and the product. HK-T05 (Hooked Ch.2) HK-T04 (Hooked Ch.2)
  2. Action. The simplest behavior done in expectation of a reward. It happens when motivation, ability and a prompt meet at the same moment, and the book tells teams to make it easier before trying to make people want it more. HK-ACT03 (Hooked Ch.3)
  3. Variable reward. The payoff solves the user's problem and changes from one pass to the next. It comes in three kinds: social (the tribe), material or informational (the hunt) and mastery or completion (the self). HK-RWD38 (Hooked Ch.4)
  4. Investment. The user puts in a little work (content, data, follows, reputation, skill) that makes the next pass better and sets up the next trigger. HK-INV31 (Hooked Ch.5) HK-INV25 (Hooked Ch.5)

How the loop behaves

  • It is a cycle, not a funnel: the investment sets up the next trigger and can make the next action easier and the next reward richer.
  • Prompt, action and reward without an investment form a feedback loop that changes behavior only while it runs.
  • Moving from outside prompts to self-started use takes weeks to months of frequent use, so a short read shows a leading signal, never a formed habit.
  • A weak step stops users from moving to self-started use, which is why audits look for the weakest link first. HK-T14 (Hooked Ch.6)

What it is, and what it isn't

The author presents the model as a practical, non-exhaustive tool rather than a validated theory Evidence grade D. Practitioner framework or anecdote: plausible, untested.. Its parts rest on evidence of different strength: repetition in a stable context builds habits (strong), endowed progress and the IKEA effect (moderate), and the full four-step sequence (untested as a whole). Book statistics come from 2010-2014 and are dated.

How we use it

The five questions the book asks of a product (internal trigger, external trigger, action, reward, investment) structure the Hook lens. The five-link scorecard and its anchors are our construct [Analyst]; see the Hook scorecard entry.

The short exercises that close each chapter build on one another, from choosing the habit to testing it, and give the order of the Hooked track: business fit and the Habit Zone, then triggers, action, reward, investment and Habit Testing. HK-T20 (Hooked Ch.1)

Limits

What we don’t claim

  • The Hook Model is a practical design tool, not a validated or complete theory of behavior.Hooked, Introduction
  • Habit metrics need the longer habit horizon (weeks to months) before they can be read.

Sources

  • Hooked · Nir Eyal

    Intro · Ch.1 · Ch.6

Source IDs: HK-T20

Book content is paraphrased, never quoted at length. Last verified October 24, 2026.

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