Sample frameDay 024·Product · Behaviour

Morning. Every habit-forming product runs the same four-step loop. Most builders miss step four.

Product.

The Hooked Model

5 min read·Apply by lunch

The question

Does your product bring users back without paid triggers — and if not, which step in the loop is broken?

The idea

The Hooked Model was developed by Nir Eyal, first in a blog post and then in his 2014 book 'Hooked: How to Build Habit-Forming Products.' Eyal synthesised research from behavioural psychology, UX design, and product strategy into a four-step cycle: Trigger → Action → Variable Reward → Investment. The model explains how products move from requiring external prompting (a paid ad, a push notification) to internal triggering (the user thinks of the product spontaneously, driven by an emotion or a context cue). The critical engine is the variable reward — reward schedules that are unpredictable produce far stronger and more persistent behaviour than fixed schedules, a finding from B.F. Skinner's operant conditioning research that every major social platform and many consumer apps have built into their core product loop. The investment phase is the mechanism most builders overlook: every piece of data, preference, content, or social connection a user puts into the product increases the switching cost and loads the trigger for the next cycle. The investment is what makes the hook self-reinforcing over time.

The framework

01
Trigger: external becomes internal.
External triggers are the scaffolding: push notifications, emails, ads, word of mouth. They get users into the loop before the habit forms. Internal triggers are the goal: the moment a user feels lonely and opens Instagram, bored and opens TikTok, uncertain and opens Google. Internal triggers are emotions or contexts that become associated with the product through repeated use. The product has succeeded when the user reaches for it without being prompted. The test: what emotion or context should trigger use of your product, and does using it consistently resolve that emotion or context? If not, the internal trigger will never form.
02
Action: reduce friction to the simplest behaviour.
The action is the simplest behaviour performed in anticipation of a reward — a scroll, a tap, a search, a swipe. BJ Fogg's behaviour model (Motivation × Ability × Prompt) explains why reducing friction on the action is as important as the reward itself. Instagram's infinite scroll is an action so frictionless it happens before the user consciously decides. Twitter's compose box is always visible. The design question: what is the smallest behaviour that gets the user into the reward phase? Every additional step between trigger and reward is a leak in the loop.
03
Variable Reward: unpredictability is the engine.
Fixed rewards create satiation — after a certain point, the same reward produces less response. Variable rewards resist satiation: the unpredictability keeps the behavioural loop active. Eyal identified three types: rewards of the tribe (social validation — likes, comments, follower counts), rewards of the hunt (information or resource seeking — a feed, a search result, a deal), and rewards of the self (mastery, completion, personal achievement — a streak, a level-up, a to-do check). The strongest habit loops deploy at least two. The design question: is the reward truly variable, or does the user know exactly what they're going to get?
04
Investment: loading the next trigger.
The investment phase is what distinguishes a habit loop from a one-time experience. Users invest time, data, content, social connections, reputation, or money into the product — and that investment makes the product more valuable to them specifically, increases switching cost, and loads the trigger for the next cycle. LinkedIn's network effect is an investment loop: every connection stored makes the platform more valuable and harder to leave. Spotify's taste profile, built through use, is an investment that makes the next recommendation better and the competitor's blank slate less appealing. The question for every product: what does using it once make more valuable about using it again?

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