The Hook Model is a psychological framework developed by Nir Eyal (in his book Hooked: How to Build Habit-Forming Products) that explains how successful digital products—like Instagram, TikTok, or Duolingo—create habit-forming user behavior.
It describes a four-step cycle that companies use to form habits around their products:
🧩 1. Trigger — The Cue That Starts It All
Definition: A trigger prompts the user to take action. It can be external (comes from the environment) or internal (comes from within the user).
- External triggers: Notifications, emails, buttons, ads — anything in the user’s environment prompting an action.
Example: A push notification saying “You have a new message!” - Internal triggers: Emotional states or routines that subconsciously cue behavior.
Example: Feeling bored → opening Instagram.
Goal: Over time, your product becomes tied to an internal trigger so that users return automatically.
⚙️ 2. Action — The Simplest Behavior in Anticipation of a Reward
Definition: The behavior a user performs in expectation of a reward.
According to behavioral psychology, users act when motivation, ability, and trigger converge.
- Motivation: The desire to do something (e.g., curiosity, pleasure, fear of missing out).
- Ability: How easy it is to do (fewer steps = more likely action).
Example:
Scrolling TikTok takes one swipe → low effort, instant entertainment → high likelihood of repeating.
Design principle: Make the desired action as simple and frictionless as possible.
🎁 3. Variable Reward — The Unpredictable Payoff
Definition: After the user acts, they receive a reward — but not always the same one.
Variability keeps people engaged because the outcome is unpredictable.
There are three main types of variable rewards:
- Rewards of the Tribe: Social approval, likes, comments.
- Rewards of the Hunt: Searching for information, deals, or resources.
- Rewards of the Self: Personal achievement, progress, mastery.
Example:
Opening your email inbox — sometimes you get something exciting, sometimes nothing. The unpredictability is what hooks you.
🔁 4. Investment — The User Puts Something In
Definition: The user invests time, data, effort, or social capital that increases the product’s value for them and makes returning more likely.
Examples:
- Creating a playlist on Spotify.
- Following accounts on Twitter.
- Saving notes in Notion.
These investments:
- Increase personal value (the product gets better for the user).
- Load the next trigger (e.g., more notifications or new content).
💡 The Hook Cycle in Action
Over time, these four steps create a self-reinforcing loop:
Trigger → Action → Variable Reward → Investment → (New Trigger)
As users cycle through this loop repeatedly, the product becomes part of their daily routines—a habit.
⚖️ Ethical Considerations
While the Hook Model is powerful, it must be used responsibly. Designers should:
- Build healthy habits (e.g., fitness, learning, productivity apps).
- Avoid exploiting addictive tendencies or manipulating vulnerable users.
Eyal himself advocates for “building habit-forming products that improve lives.”
🔍 Example: Duolingo’s Hook Model
| Step | Example |
|---|---|
| Trigger | Notification: “Time to practice your Spanish!” |
| Action | Opening the app and doing a quick lesson |
| Variable Reward | Earn XP, see streak grow, unlock a new skill |
| Investment | Progressing levels, maintaining streak, adding friends |
This cycle encourages daily engagement.
