In short
The Hook model is a framework by Nir Eyal that describes how products build habits through four repeating steps: trigger, action, variable reward and investment. Each pass through the loop makes the next one more likely, until users return out of habit rather than reminders.
Why it matters for apps
The Hook model gives teams a simple checklist for habit-forming design. Each step points to a concrete product decision.
- Trigger: An external cue, such as a notification, or an internal one, such as boredom, prompts use.
- Action: The simplest behavior done in anticipation of a reward. Make it fast and easy.
- Variable reward: An outcome with some unpredictability keeps interest higher than a fixed result.
- Investment: Users put in data, effort or progress that makes the product more valuable to them next time.
A common mistake is focusing only on triggers. Without a real reward and investment, more notifications just lead to more unsubscribes.
Industry examples
Duolingo sends practice reminders (trigger), asks for a short lesson (action), gives XP and leaderboard moves (reward), and builds a streak users want to keep (investment).
On Strava, an uploaded activity can collect kudos and comments from others, and each upload adds to the athlete's training history.
Build it with StriveCloud
In StriveCloud, push notifications and challenge nudges are the trigger, and events from your app are the action. Scratchcards or Wheel of Fortune spins supply the variable reward. Streaks, levels, badges and tiers are the investment users do not want to lose.
Want to try this? See the Duolingo playbook
Frequently asked questions
What are the four steps of the Hook model?
Trigger, action, variable reward and investment. Nir Eyal describes them in his book Hooked as a loop that builds habits over repeated use.
What is the difference between the Hook model and a habit loop?
The classic habit loop has cue, routine and reward. The Hook model adds variable rewards and an investment step that makes the product better with use.
Is the Hook model ethical?
It can be used well or badly. Nir Eyal suggests asking whether the product genuinely improves users' lives and whether you would use it yourself.