Design habit-forming product loops using the Hook Model (Trigger, Action, Variable Reward, Investment). Use when the user mentions "users aren't coming back", "engagement loops", "habit formation", "push notifications", or "variable rewards". Covers ethics evaluation and onboarding for habits. For friction reduction and B=MAP, see improve-retention. For viral sharing, see contagious.
Design habit-forming product loops using the Hook Model (Trigger, Action, Variable Reward, Investment). Use when the user mentions "users aren't coming back", "engagement loops", "habit formation", "push notifications", or "variable rewards". Covers ethics evaluation and onboarding for habits. For friction reduction and B=MAP, see improve-retention. For viral sharing, see contagious.
license
MIT
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{"author":"wondelai","version":"1.1.1"}
Hook Model Framework
Framework for building habit-forming products. Based on a fundamental truth: habits are not created—they are built through successive cycles through the Hook.
Core Principle
The Hook Model = a four-phase process that connects the user's problem to your solution frequently enough to form a habit.
Habit Zone: Products enter the "habit zone" when used frequently enough and with enough perceived value. The goal is to move users from deliberate usage to automatic, habitual behavior.
Scoring
Goal: 10/10. When reviewing or creating product engagement mechanics, rate them 0-10 based on adherence to the principles below. A 10/10 means full alignment with all guidelines; lower scores indicate gaps to address. Always provide the current score and specific improvements needed to reach 10/10.
The Four Phases
1. Trigger
Core concept: The actuator of behavior. What prompts the user to take action? Triggers come in two forms: external (environment-driven) and internal (emotion-driven). The ultimate goal is to move users from external triggers to internal triggers.
Why it works: Every habit starts with a cue. Without a trigger, there is no behavior. External triggers get users started, but internal triggers — emotions like boredom, loneliness, uncertainty, or fear of missing out — are what drive unprompted, habitual usage. When your product becomes the automatic response to an internal trigger, you have a habit.
Key insights:
External triggers (push notifications, emails, buttons, ads, word of mouth) initiate behavior early on
Internal triggers (emotions, routines, situations) are the ultimate goal — users prompt themselves
The goal is to move users from external triggers to internal triggers over time
Map your product to the specific negative emotion it resolves (boredom, loneliness, confusion, FOMO)
Effective external triggers must be well-timed, actionable, and lead to the simplest possible next action
Product applications:
Context
Application
Example
Onboarding
Use external triggers to establish first loop
Welcome email with one clear action to take
Retention
Map product to internal emotional trigger
Instagram resolves boredom; Google resolves confusion
Re-engagement
External triggers bridge gaps until habit forms
Push notification: "Your friend just posted a photo"
Emotion mapping
Identify which negative emotion your product addresses
If yes after 30 days, internal trigger hasn't formed
Copy patterns:
"You might be wondering about..." (hooks into uncertainty)
"Don't miss what happened while you were away" (FOMO trigger)
"Your friend just..." (social/external trigger bridging to internal)
"Pick up where you left off" (routine trigger)
Notification copy should name the emotion: "Curious what's new?"
Ethical boundary: Never exploit vulnerable emotional states (depression, addiction, grief) as triggers. Triggers should connect users to genuine value, not manufacture anxiety to drive opens.
See: references/triggers.md for detailed trigger design, emotion mapping, and external-to-internal transition strategies.
2. Action
Core concept: The simplest behavior done in anticipation of a reward. Guided by the Fogg Behavior Model: B = MAT (Behavior = Motivation + Ability + Trigger). All three must converge at the same moment for action to occur.
Why it works: Increasing motivation is hard and unreliable. Reducing friction (increasing ability) is easier and often more effective. The key insight is that making the action simpler is almost always a better strategy than trying to increase motivation. Every extra step, field, or decision is a point where users drop off.
Key insights:
Fogg Behavior Model: Behavior = Motivation x Ability x Trigger — all three must be present simultaneously
Six elements of simplicity (ability): time, money, physical effort, brain cycles, social deviance, non-routine
Increasing ability (reducing friction) is almost always more effective than increasing motivation
The action should be the simplest behavior in anticipation of the reward — not the full task
Hick's Law: more choices = slower decisions; reduce options to increase action rate
Product applications:
Context
Application
Example
Signup flow
Minimize fields and steps to reduce friction
One-click Google/Apple sign-in instead of form
Core action
Make the key behavior completable in seconds
Twitter: type 280 characters and post (vs. write a blog)
Simplicity audit
Evaluate each of the six ability factors
Can user complete core action in under 60 seconds?
"We've set up defaults for you" (brain cycle simplicity)
Buttons should be verbs: "Post", "Save", "Share" — not "Submit" or "Continue"
Ethical boundary: Reducing friction should make genuinely valuable actions easier — not trick users into actions they'd regret. Dark patterns that hide costs or consequences behind simple actions are unethical.
Core concept: The phase that keeps users coming back. The anticipation of reward — not the reward itself — creates dopamine. Critically, rewards must be variable (unpredictable) to maintain engagement. Predictable rewards lose their power over time.
Why it works: The brain's dopamine system responds most strongly to the anticipation of uncertain rewards, not to the rewards themselves. This is the slot machine effect: variable reinforcement schedules are far more engaging than fixed ones. Three types of variable rewards — tribe (social), hunt (resources), and self (mastery) — tap into fundamental human drives.
Key insights:
Dopamine spikes during anticipation of uncertain reward, not upon receiving it
Three types: Tribe (social validation), Hunt (search for resources/information), Self (personal mastery)
Predictable rewards lose power; variability is what sustains engagement
The "slot machine effect": uncertainty is what makes rewards compelling
Autonomy is critical — users must feel in control; forced engagement backfires
Finite variability (limited content) eventually becomes predictable; aim for infinite variability
Product applications:
Context
Application
Example
Social features (Tribe)
Variable social validation from others
Instagram likes, Reddit upvotes — you never know how many
Content feeds (Hunt)
Unpredictable stream of resources/information
Infinite scroll with algorithmically varied content
Gamification (Self)
Personal accomplishment with variable difficulty
Duolingo streaks + surprise bonus challenges
Notifications
Variable content in each notification
"3 people liked your post" vs. "Sarah commented something surprising"
Search/Discovery
The hunt for the next great find
Pinterest: scroll to find the perfect pin; eBay: hunt for deals
Copy patterns:
"See what's new" (implies variability — you don't know what you'll find)
"You won't believe what happened next" (curiosity + variable reward)
"3 people responded to your post" (tribe reward, variable quantity)
"You've unlocked a new achievement!" (self reward, unexpected)
"Trending now..." (hunt reward — the feed changes every time)
Ethical boundary: Variable rewards should deliver genuine value, not exploit compulsive behavior. If users consistently feel worse after engaging (regret, time loss, anxiety), the reward system is extractive, not valuable. Avoid infinite scroll without natural stopping points for vulnerable users.
See: references/rewards.md for reward design patterns, reinforcement schedules, and reward timing.
4. Investment
Core concept: The phase that increases the likelihood of another pass through the Hook. Users invest something — time, data, effort, social capital, or money — that improves the product for next use and raises switching costs. Investment loads the next trigger.
Why it works: People value what they put effort into (the IKEA effect). Investment creates stored value that makes the product better with use and harder to leave. Critically, investment is not about immediate reward — it's about improving the next cycle. Each investment loads the next trigger, creating a self-reinforcing loop.
Key insights:
IKEA effect: users value what they invest effort into, even irrationally
Investment creates switching costs (data, content, reputation, skill, social connections)
Investment should come after reward, not before — users invest when they feel good
Each investment should load the next trigger (creating content triggers notifications when someone responds)
Small investments compound: preferences lead to better recommendations lead to more usage
Stored value increases over time, making the product harder to leave
"Personalize your experience" (inviting data investment)
"Complete your profile to get better matches" (investment → future value)
"Invite your team to collaborate" (social investment)
"The more you use it, the smarter it gets" (compound investment)
"Your history, preferences, and connections — all in one place" (switching cost reminder)
Ethical boundary: Investment should genuinely improve the user's experience. Don't make data export impossible or trap users with artificial switching costs. Ethical products let users leave with their data while making staying the better choice through real value.
Nir Eyal is an author, lecturer, and investor who has taught at Stanford Graduate School of Business and the Hasso Plattner Institute of Design at Stanford. He previously worked in the gaming and advertising industries, where he gained firsthand experience with the psychology of habit-forming products. Hooked distills years of research and consulting into a practical framework used by product teams at startups and Fortune 500 companies worldwide. His follow-up book, Indistractable, addresses the other side of the equation — helping individuals manage the same behavioral triggers that make products habit-forming. Eyal writes extensively about the intersection of psychology, technology, and business at NirAndFar.com.
