What is the Hook Model?
The Hook Model is Nir Eyal's four-stage loop of trigger, action, variable reward and investment. This piece walks through each stage in turn and sets beside it the research it draws on.
Answer to the question
What is the Hook Model?
The Hook Model is Nir Eyal's four-stage loop for how a product becomes part of a routine: a trigger prompts a simple action, a reward that varies follows, and the person then makes an investment that sets up the next trigger. Eyal set it out in his 2014 book Hooked, building on B.J. Fogg's behaviour model.
Key takeaways
- Nir Eyal's Hooked (2014) gives the Hook Model four stages, trigger, action, variable reward and investment, run as a loop that is meant to repeat.
- Gollwitzer and Sheeran (2006) pooled 94 independent tests and found that if-then plans tying a cue to a response raised goal attainment by a medium-to-large amount.
- Freedman and Fraser (1966) found that people who agreed to a small request were more likely to agree to a larger one, whether the same person or a different person asked.
- Lally and colleagues (2010) followed 96 volunteers for 12 weeks; the time to reach 95 per cent of each person's plateau of automaticity ranged from 18 to 254 days.
Nir Eyal's 2014 book Hooked gave product makers a four-stage loop of trigger, action, variable reward and investment, repeated until a product becomes part of a routine.
That loop is the Hook Model. B.J. Fogg had published a behaviour model for persuasive design, and Eyal built on that line of thinking; the updated edition of the book kept the diagram unchanged. Eyal drew its stages from older research and from case stories.
How the loop starts, from outside cue to inner feeling
Does the Hook Model Actually Work asks whether the loop holds up as a whole. The model itself runs in a circle. A trigger prompts a person to do something. The action is the smallest step that follows. A reward arrives, and its size or kind varies from one visit to the next. The person then puts something into the product, and that contribution sets up the next trigger. Eyal presented the loop in 2014 as a design framework, a map assembled from practice and from borrowed research, not a result from a single experiment.
| Term | Eyal's meaning |
|---|---|
| Trigger | The cue that starts the loop, either outside the person or felt inside |
| Action | The simplest behaviour done in expectation of a reward |
| Variable reward | A payoff whose size or kind is not fixed in advance |
| Investment | Effort, data or content the person puts in, which loads the next trigger |
| Stored value | What builds up from investment and makes the product better with use |
Eyal sorts external triggers into four kinds: paid, earned, relationship and owned. Owned triggers, such as an email or a notification from an app the person chose to install, are cheap enough to fire again and again, so the Hook Model leans on them. The aim is that the cue eventually moves inside the person. An internal trigger is a feeling or a situation, such as boredom or uncertainty, that prompts use with no outside prompt at all.
Research on planned cues gives the idea a parallel. Peter Gollwitzer and Paschal Sheeran reviewed 94 independent tests of implementation intentions, which are if-then plans naming when, where and how to act. The pooled effect on goal attainment was of medium-to-large size, and the authors reported support for two processes: the named opportunity becomes easier to notice, and the linked response becomes more automatic. A cue joined to a response is what a trigger is meant to be, with one difference: in those studies the person writes the plan, and in Eyal's loop the product sends the cue.
Why the step is small and the payoff uncertain
For the second stage of the Hook Model Eyal adopts Fogg's model, in which a behaviour happens when motivation, ability and a prompt arrive together. Of the three, he treats ability as the lever a designer can pull most cheaply, since removing effort costs less than raising desire. He lists six ways an action can be hard: time, money, physical effort, mental effort, social deviance and departure from routine.
A one-tap sign-in takes away time and mental effort. A saved payment detail takes away money and a pause to think. A feature that works the way other apps already work takes away departure from routine. In the Hook Model the action stage is therefore a subtraction exercise, and the question a maker asks of it is how many of the six remain.
Recordings of dopamine neurons in a 2003 report from the laboratory of Wolfram Schultz began with cues that signalled the probability of a reward. Activity changed steadily across the whole range of probabilities, and a second response rose gradually towards the expected time of the reward and tracked uncertainty. The authors suggested the finding may bear on attention-based learning and on risk-taking.
Uncertainty about the payoff is also the centre of the third stage, variable reward. Eyal describes three families of reward: social approval, material resources or information, and a sense of mastery or completion, and Why Loyalty Apps Use Random Rewards follows the same stage into loyalty schemes. What the families share is that the person cannot be sure in advance what the next visit will bring. He also separates a supply of novelty that runs out once a person has explored it from a supply that other people keep refilling, and he expects the second kind to last longer.
What the person leaves behind and how habits form
Phillippa Lally and colleagues followed 96 volunteers who each chose a daily eating, drinking or activity behaviour and did it in the same setting for 12 weeks, rating how automatic it felt every day. The time to reach 95 per cent of each person's plateau of automaticity ranged from 18 to 254 days. Missing a single opportunity made no material difference to the process.
Eyal argues that the fourth stage of the Hook Model separates a loop from a straight line. Here the person puts something in: data, content, followers, a reputation or a skill, and Why You Love the Thing You Assembled covers the effort-and-valuation side of this stage. The stored value tends to improve the product with use, which raises the cost of leaving and loads the next trigger. A saved item or a reply from a follower gives the product a reason to ask the person to return.
The commitment research Eyal leans on at this stage includes the 1966 experiments of Jonathan Freedman and Scott Fraser. They tested whether someone who has agreed to a small request becomes more likely to agree to a larger one, and found the effect, now called foot-in-the-door, both when the same person made the two requests and when different people did. Applied to a product, the small request would be a rating, a saved preference or a filled-in profile, and the larger one the next visit, though the experiments tested requests and not ratings.
Eyal's design is meant to repeat, and the Lally study places the formation of a habit in that repetition, across a span that differs widely between people. One trip round is a prompt, a step, a payoff and a deposit. By Eyal's account, the cue has done its work once the person feels it. The product no longer has to send it.
Common questions
What is the Hook Model?
The Hook Model is Nir Eyal's loop of trigger, action, variable reward and investment. A cue prompts a simple action, a reward of varying size follows, and the person then puts something into the product that sets up the next cue.
Who created the Hook Model?
Nir Eyal set it out in his 2014 book Hooked. He built on B.J. Fogg's 2009 behaviour model, in which a behaviour needs motivation, ability and a prompt together.
Does a variable reward mean a random reward?
Not in Eyal's account. He describes variability as a payoff whose size or kind is not fixed in advance, with social, material and personal families of reward.
Sources
Eyal, N. (2014). Hooked: How to Build Habit-Forming Products. Portfolio. Seed book; vault hub Books/Hooked.
Fogg, B. J. (2009). “A behavior model for persuasive design.” Proceedings of the 4th International Conference on Persuasive Technology, Article 40. doi:10.1145/1541948.1541999 https://doi.org/10.1145/1541948.1541999
Gollwitzer, P. M., & Sheeran, P. (2006). “Implementation intentions and goal achievement: A meta-analysis of effects and processes.” Advances in Experimental Social Psychology, 38, 69-119. doi:10.1016/S0065-2601(06)38002-1 https://doi.org/10.1016/S0065-2601(06)38002-1
Fiorillo, C. D., Tobler, P. N., & Schultz, W. (2003). “Discrete coding of reward probability and uncertainty by dopamine neurons.” Science, 299(5614), 1898-1902. doi:10.1126/science.1077349 https://doi.org/10.1126/science.1077349
Freedman, J. L., & Fraser, S. C. (1966). “Compliance without pressure: The foot-in-the-door technique.” Journal of Personality and Social Psychology, 4(2), 195-202. doi:10.1037/h0023552 https://doi.org/10.1037/h0023552
Lally, P., van Jaarsveld, C. H. M., Potts, H. W. W., & Wardle, J. (2010). “How are habits formed: Modelling habit formation in the real world.” European Journal of Social Psychology, 40(6), 998-1009. doi:10.1002/ejsp.674 https://doi.org/10.1002/ejsp.674