Does Your Product Have a Hook?

From the Jason Calacanis startup checklist. Based on Hooked by Nir Eyal.

Nir Eyal's Hook Model describes how great products create habits through a four-stage cycle:

The Four Stages

1. Trigger — something that prompts the user to take an action. What makes you open an app in the first place? Triggers can be external (a notification, a link on another platform) or internal (boredom, anxiety, curiosity).

2. Action — the simplest behaviour the user can perform in anticipation of a reward. The key is to have as little friction as possible here. The easier the action, the more likely users are to complete it.

3. Variable Reward — the keyword is variable. If users always know exactly what they'll get, they lose interest. Unpredictability keeps them engaged and coming back.

4. Investment — the user puts something into the product (time, data, social capital, content) that makes the product more valuable to them and increases switching costs.

Pinterest Example

Stage	What happens
Trigger	A link to a Pinterest image appears on Facebook or Instagram
Action	User clicks the link and opens Pinterest
Variable Reward	They discover a feed of similar products and images — always different
Investment	User pins items they like, giving Pinterest better data for future recommendations

Fitbod Example

Fitbod's co-founder Jesse Venticinque described the product's hook cycle on Scaling Your Startup (Season 2, Episode 5):

Stage	What happens
Trigger	Psychological need to exercise effectively; Fitbod auto-generates a new workout
Action	User opens Fitbod to start their session
Variable Reward	Incremental, achievable goals that leave users feeling accomplished
Investment	Users log workout data, which improves personalisation, increases switching costs, and reduces churn

When the workout ends, Fitbod immediately generates the next one — restarting the cycle. That's the hook.