From his book Hooked, Nir Eyal's model describes a four-step loop that habit-forming products run their users through, repeatedly, until the behavior becomes automatic — matching the "habit" end of Fogg's Behavior Grid from the previous lesson.
| Step | What it is | Example |
|---|---|---|
| 1. Trigger | External (a notification) or internal (boredom, loneliness) cue that starts the loop | A message notification; the internal urge to check for updates |
| 2. Action | The simplest behavior done in anticipation of a reward | Opening the app, scrolling the feed |
| 3. Variable Reward | A reward whose exact content or size isn't fully predictable | Not knowing what the next post, like count, or message will be |
| 4. Investment | The user puts something in — data, content, followers, effort — that makes the product more valuable next time | Posting content, building a follower list, customizing a profile |
A predictable reward loses its pull quickly — a slot machine and a vending machine both dispense something, but only one is designed to keep someone pulling the lever. Variability (not knowing exactly what's coming) is what makes step 3 psychologically sticky, borrowed directly from behavioral psychology research on reward schedules.
The Investment step is what turns a single use into a habit loop — a user who has built a profile, a follower list, or a history of saved content has a reason to come back that a brand-new user doesn't. Each pass through the loop, done well, seeds the next Trigger (a new follower, a reply to a comment) automatically.
Where this gets ethically risky
This exact model, used without restraint, is also the mechanism behind genuinely addictive product design — infinite scroll, unpredictable notification timing, and engagement metrics chased for their own sake. The next lesson draws the ethical line the Hook Model itself doesn't draw.