The Hook Model
How products create habits—Trigger, Action, Variable Reward, Investment. The psychology behind addictive products.
Nir Eyal's Hook Model, introduced in his 2014 book "Hooked," explains how products create habits. Drawing from behavioral psychology and consumer neuroscience, Eyal codified the four-step cycle that turns casual users into habitual ones: Trigger → Action → Variable Reward → Investment. The framework has become essential reading for product designers, growth teams, and anyone building engagement-driven products. It's also sparked ethical debates about manipulation vs. value creation.
Trigger
The actuator of behavior—prompts users to take action. Can be external (notifications, emails, ads) or internal (emotions, routines, situations).
External triggers: Push notifications, app icons, email reminders, social invites.
Internal triggers: Boredom (Instagram), loneliness (Facebook), uncertainty (Google).
Action
The simplest behavior done in anticipation of reward. Action follows Fogg's formula: B = MAT (Behavior = Motivation × Ability × Trigger). The easier the action, the more likely it happens.
Examples: Scrolling a feed, swiping right, tapping a notification, typing a search query, pulling to refresh.
Variable Reward
Unpredictable reinforcement that satisfies the user's need while leaving them wanting more. Variability creates dopamine spikes and keeps users engaged longer than fixed rewards.
Examples: New likes/comments (variable social validation), feed refresh revealing new content (variable novelty), loot boxes in games (variable prizes).
Investment
User puts something into the product that improves it with use and makes it harder to leave. Investment loads the next trigger and increases likelihood of returning.
Examples: Adding content (posts, photos, playlists), building followers, customizing profiles, inviting friends, storing data, completing profiles.
The hook cycles continuously. Each loop strengthens the habit. Products that master this cycle create user dependency—for better or worse.
Social rewards—acceptance, validation, status, belonging. Driven by our need for social connection and recognition from others.
Examples: Likes on Instagram, upvotes on Reddit, retweets on Twitter, followers on TikTok, kudos on Strava.
Material rewards—information, money, resources. Driven by our need to acquire things and gather information to survive and thrive.
Examples: Feed scrolling (hunting for interesting content), email checking (hunting for important messages), deal hunting on Amazon, job hunting on LinkedIn.
Intrinsic rewards—mastery, completion, competence, consistency. Driven by our need for self-improvement and control over our environment.
Examples: Duolingo streaks, fitness tracking progress, clearing email inbox to zero, leveling up in games, completing achievements.
Best For:
- Products requiring frequent, unprompted engagement
- Building retention and daily active usage
- Consumer apps, social platforms, games, health/fitness products
- Diagnosing why users don't return to your product
- Designing onboarding and engagement loops
- Understanding competitive products' stickiness
Less Effective When:
- Products are infrequent-use (insurance, tax software)
- B2B tools where usage is obligation, not choice
- Transactional products without repeat behavior
- Ethical concerns outweigh engagement goals
- Building habits conflicts with user wellbeing
The Hook Model is powerful—and that power can be misused. Eyal himself emphasizes the "Manipulation Matrix": only use hooks to build products that materially improve users' lives and that you'd use yourself. Creating habits for harmful behaviors (gambling, doomscrolling, unhealthy consumption) is manipulation, not product design. The framework should help people, not exploit psychological vulnerabilities. Use responsibly.
External: Red notification badges, push notifications. Internal: Boredom, FOMO, desire for social connection.
Open app, scroll feed. Extremely low friction—takes 1 second from lock screen to content consumption.
Tribe: Variable likes, comments, followers. Hunt: Scrolling reveals unpredictable interesting content. Self: Seeing your own post perform well.
Posting photos, building followers, customizing profile, creating Stories, saving posts, following accounts. Each investment makes leaving harder.
External: Message notifications, @mentions, channel activity. Internal: Fear of missing work updates, need to stay responsive.
Open Slack, check messages. Desktop app and mobile ensure immediate access. Low friction to check "what's new."
Hunt: Messages might be urgent, interesting, or routine—unpredictability drives checking. Tribe: Social validation from team responses.
Creating channels, building workflows, integrating tools, storing conversations, adding custom emojis. The more invested, the harder to switch platforms.
External: Push notifications ("Don't lose your streak!"), email reminders, app icon badge. Internal: Guilt about not practicing, desire for self-improvement.
Start a 5-minute lesson. Extremely low barrier—bite-sized lessons make action easy even when motivation is low.
Self: Streak maintenance, XP progress, level-ups. Hunt: Unlock new content, earn gems. Tribe: Leaderboard competition with friends.
Building streak count (loss aversion kicks in), personalizing avatar, joining leagues, following friends, completing skill trees. Investment creates sunk cost.
External: Video recommendations, email notifications for new uploads, push alerts. Internal: Boredom, curiosity, desire to learn/be entertained.
Click a video. Autoplay ensures the next video starts without action. Friction is eliminated—consumption becomes passive.
Hunt: Next video might be amazing or mediocre—algorithm unpredictability keeps you watching. Self: Learning new things. Tribe: Comments section engagement.
Subscribing to channels, liking videos (teaches algorithm), creating playlists, commenting. Investment personalizes recommendations, making YouTube more valuable over time.
Nir Eyal is a behavioral design consultant, author, and former Stanford lecturer who spent years studying why some products become habits while others fail. His 2014 book "Hooked: How to Build Habit-Forming Products" synthesized research from behavioral psychology (B.F. Skinner's variable rewards), consumer neuroscience (dopamine loops), and his own consulting experience with startups.
Eyal's insight: successful products don't rely on willpower or constant marketing—they create automatic behaviors. The Hook Model gave product designers a framework to engineer habits intentionally, not accidentally. The book became required reading in Silicon Valley, taught at Stanford, and influenced products with billions of users.
Eyal later wrote "Indistractable" (2019) to address criticism that he'd created a playbook for manipulation. His position: hooks should improve lives, not exploit them. The framework is amoral—a tool that can build wellness apps or slot machines. Responsibility lies with designers, not the model.
Mobile-First Era (2010s): The Hook Model emerged when smartphones became dominant. Apps competed for attention in users' pockets—push notifications, red badges, infinite scroll. Eyal codified what winning apps were already doing intuitively. The framework explained why Facebook, Instagram, and Snapchat were sticky while thousands of competitors failed.
Freemium Business Models: Hooks became essential when products moved from paid to freemium. If users don't pay upfront, retention is everything. Habitual use drives monetization—through subscriptions, ads, or in-app purchases. The Hook Model showed how to build retention without constant marketing spend.
The Techlash (Late 2010s): As social media's downsides became clear—addiction, polarization, mental health impacts—Eyal's framework faced criticism. Critics called it a manipulation playbook. Defenders argued it's just behavioral science applied to product design. The debate highlighted the ethical responsibility of designers: are you creating value or exploiting vulnerabilities?
Why It Endures: The Hook Model survives because it describes reality. Habits are formed through triggers, actions, rewards, and investments—whether designed intentionally or not. The framework makes implicit patterns explicit. Product teams use it to build retention, understand competitors, and diagnose engagement problems. The ethics matter, but the psychology is universal. Hooks aren't going away—the question is how we use them.