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Hooked · Nir Eyal

The Hook Model

How products earn repeat use: a trigger, an action, a reward that varies and an investment that sets up the next pass.

Evidence grade D. Practitioner framework or anecdote: plausible, untested.144 techniques in the libraryVerified October 24, 2026

Teams use the Hook Model to design products people come back to without being pushed. It describes a loop with four steps, repeated until the product becomes the first thing someone reaches for.

We use it as a lens, not a law: to find the weakest step in a product’s loop and decide what to fix first. The book’s own author presents it as a practical tool, and so do we.

Evidence grades across the 144 techniques in our library that map to this framework:

Evidence grades across 150 graded items: 1 grade A (robust), 32 grade B (moderate), 42 grade C (limited), 75 grade D (practitioner).

four-step habit loop

In plain English

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.

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)

The full entry: The Hook Model

Hook Model

The four steps

Each step, in plain English, with the techniques in our library that work on it and how strong their evidence is.

  1. 01

    Trigger

    Something prompts the behavior: a message or a button at first, later a feeling or a routine.

    Evidence grades across 36 techniques: 3 grade B (moderate), 11 grade C (limited), 22 grade D (practitioner).

    36 techniques, strongest evidence first

    Show 32 more techniques16 more techniques in the knowledge base

  2. 02

    Action

    The simplest thing a person does expecting a reward. Make it easier before making people want it more.

    Evidence grades across 37 techniques: 14 grade B (moderate), 13 grade C (limited), 10 grade D (practitioner).

    37 techniques, strongest evidence first

    Show 33 more techniques17 more techniques in the knowledge base

  3. 03

    Variable reward

    The payoff solves the problem and changes a little each time, so people come back to see what they get.

    Evidence grades across 31 techniques: 5 grade B (moderate), 8 grade C (limited), 18 grade D (practitioner).

    31 techniques, strongest evidence first

    Show 27 more techniques11 more techniques in the knowledge base

  4. 04

    Investment

    A small bit of work (data, content, follows, skill) that makes the next pass better and loads the next trigger.

    Evidence grades across 34 techniques: 9 grade B (moderate), 7 grade C (limited), 18 grade D (practitioner).

    34 techniques, strongest evidence first

    Show 30 more techniques14 more techniques in the knowledge base

Limits

What we don’t claim

These caveats travel with the frameworks everywhere they appear, on this site and in every answer Gamify It gives in your AI assistant.

  • The Hook Model is a practical design tool, not a validated or complete theory of behavior.Hooked, Introduction
  • Octalysis is a practitioner framework built from observing games, not a validated scientific model.Actionable Gamification Ch.15, pp.399-400
  • Left Brain and Right Brain are a metaphor for extrinsic and intrinsic motivation, not a claim about neuroscience.Actionable Gamification Ch.13, pp.342-343
  • Habit metrics need the longer habit horizon (weeks to months) before they can be read.
  • The threshold is a heuristic, not a measured cut-off.
  • This is a practitioner heuristic (grade D): test it in your own product before relying on it.
  • The evidence is correlational until it is tested in your product.

Go deeper

More from the knowledge base

  • Framework · The Hook Model

    The Habit Zone

    frequency and usefulness threshold

    A behavior becomes a default only when it happens often enough and feels useful enough compared with the alternatives. Frequency can make up for modest usefulness, but a behavior that is too rare stays a conscious choice however useful it is. The model deliberately has no numeric scale.

  • Framework · The Hook ModelEvidence grade D. Practitioner framework or anecdote: plausible, untested.

    Habit Testing: identify, codify, modify

    find, map and spread the habit

    A repeating loop for proving habits with data. Identify a realistic cadence for a devoted user and who meets it, codify the early steps those users share, then modify the product to send new users down that path, and measure again. Ideas from the Hook Model are only hypotheses until this loop tests them.

  • Framework · The Hook ModelEvidence grade D. Practitioner framework or anecdote: plausible, untested.

    Hook scorecard: five links, scored 0-5

    five-link habit loop audit

    An audit built on the book's five questions about a product: what users really want relief from, what brings them back, the simplest action, whether the reward satisfies yet leaves them wanting more, and what they invest. We split the trigger into internal and external and score each link from 0 to 5; the lowest link is the next thing to fix.

Sources

Source IDs: HK-T20HK-T02HK-STR02HK-T01F15HK-T16HK-MEA01HK-MEA02HK-MEA03HK-MEA04HK-MEA05HK-T14HK-MEA07

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

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