Simplified: Hooked by Nir Eyal

A psychology book that focuses on how to build products.

Human behaviour can be studied, products can exploit its nature and hence value can be derived, but we should be careful where we are making things addictive and habitual. There is a continuous loop you may want to build if you believe it is the right thing to do: have a trigger, have an action, provide a (potentially variable) reward, have the user invest and then provide another trigger.

The hooked model

The premise of the book focuses on creating an endless loop of human behaviour through the instantiation of:

  • A trigger (an external recommendation or, later, an internal need),
  • An action (which a reward is anticipated)
  • A variable reward is given (which creates a craving)
  • And then an investment that will make it better next time (invite friends, personalisation or assets)

If a product allows you to build a habit then your reoccurrence is suddenly improved as this cycle becomes more frequent.


David Skok states:

“The most important factor to increasing growth is Viral Cycle Time. Viral Cycle Time is the amount of time it takes a user to invite another user, and it can have a massive impact. For example, after 20 days with a cycle time of two days, you will have 20,470 users. But if you halved that time to one day you would have over 20 million!”

How much better

John Gourville shows that if a new entrant is to beat an established player it must be 9x more valuable. Why? Because routines, learning and behaviour are hard to change without warrant.

The Habit Zone

You must recognise whether your product sits in the habit zone to see if the hooked model will apply well. This means you need your users to show how often they use the service and how much perceived utility there is (compared to alternative solutions).

Hooked Model #1: Trigger

  • Paid Trigger – essentially SEO and ads
  • Earned Trigger – like app store ratings and press
  • Relationship Trigger – referrals, peer to peer (but doing this against users will lose trust)
  • Owned Triggers – triggers that come from the product you own (and hence can be the most powerfully – think Duolingo notifications)
  • Habits essentially – what your mind does unprompted. When you are bored do you immediately go to Facebook? More often than not, a negative feeling is a strong trigger of action.

“Ask yourself what pain these habits solve and what users might be feeling right before one of these actions. What would your users want to achieve by using your solution? Where and when will they use it? What emotions influence their use and will trigger them to action?”

Essentially build empathy maps and user studies.

Evan Williams, co-founder of Blogger, Twitter and Medium, says ‘Take a human desire, preferably one that has been around for a really long time… and use modern technology to solve it.’

Hooked model #2: Actions

  • Time
  • Cost
  • Labour
  • Mental effort
  • Social deviance/pressure
  • Disruption to routine


  • Logging in – the more steps, the more time, the more effort. Having one-click account creation improves this, but you still need to test it
  • Sharing – preformatting and summarising can help save effort and time
  • Decluttering – simplifying your page for the single route of value
  • Scrolling – infinite pages reduced effort and hence became a big hit
  • Make things scarce and they will be more valuable i.e. showing the user a product is low in stock may encourage them to buy it in quicker time.
A Prime Example ;)
  • Framing – the bottle size determines the price
  • Anchoring – £50 down to £30 is much better than the non-discounted £30 one
  • Progress – if a loyalty card starts at 2 and goes to 8, it is more enticing than one that starts on 0 and goes to 6. LinkedIn has a profile strength indicator that will never start at 0%.

Hooked model #3: Reward

‘What draws us to act is not the sensation we receive from the reward itself, but the need to alleviate the craving for that reward’

Evolutionarily, this is beneficial as it encourages curiosity and investigation.

  • Of the tribe – the feeling of acceptance, important and being included. Essentially watching that show, having that thing, joining that group, being recognised. Think rep, think likes, think karma.
  • Of the hunt – our brains are designed for motivation during a chase as evolutionary we engaged in persistence hunting. Think playing to win, think searching.
  • Of the self – a desire for competency which we may not even be enjoying the journey to. Think climbing the mountain as opposed to being lifted to the top, think solving the huge jigsaw or puzzle, despite hours of frustration.

Often rewards are not monetary – gamification can help too. But ultimately it must fit the purpose, else users will not be motivated by it.

If the reward is not infinitely variable, users will get used to it and it will become boring. Games recognised this by letting multiple players play one another. YouTube has user-generated content to keep things fresh.

When user journeys already have some variability – think search results or ride-sharing – you don’t want more variability and as such you must control this well. If the user is in full control, variability can be fun.

A test of pigeons pulling on a lever to get food showed that when the release of food was predictable, the lever was used much less. When it was random, it was used much more.

Hooked Model #4: Investment

If you build it, you tend to love it more. This is the IKEA or build-a-bear effect. When you put time into something, you see it as more valuable and this is why you want users to impart some labour.

Little investments can be grown better than larger ones. A study where people were asked to put a large sign in their garden proved that if you already had a small sign you were likely to oblige, whereas those without a sign were more reluctant. Similarly, if you asked someone to marry you on the first date, you would be unlikely to get a positive response.

  • Content – like Facebook having images or Spotify generating playlists.
  • Data – like LinkedIn with resume data
  • Followers
  • Reputation
  • Skill – learning the software will make it ‘sticky’

Hooked Model #5? Loop

That is it. As soon as the user has invested, there should be a growing motivation to use it again.

Now what? Oh yeah, responsibility!

You can recognise internal triggers or needs, ideate for external triggers to your service, define the first reward a user will get, define whether it should be variable and what bit of work the user needs to do to invest.

But should you? People have died from addiction to products, others are innocuous but where do the morals sit? If you can manipulate behaviour, should you?

We haven’t had time to develop antibodies to addictive new things – Paul Graham

Facilitators are at the top right of the matrix and the manipulation technique you want to aim for. They make peoples lives better and the creators use their own product. I think of companies like Strava or Zwift.

Peddlers have the desire to help users but do not use their product and such there can be a mismatch in what is built and what is wanted.

Entertainers make art. When art becomes addictive it is often fleeting, think pop songs; however, they do make a meaningful addition to the human experience.

Dealers exploit. They do not believe it makes a difference to a users life and they do not use it themselves. For example, where do you sit with cigarettes?

This concept reminds me of Ikigai.


Defining habitual behaviour

  1. Identify – define what a habitual user does, how often and find them
  2. Codify – see the habitual users journey and measure it to see what the critical action is that builds a habitual user
  3. Modify – track and change (using cohort analysis)

Where opportunity lies

  • Tech change – if a technology is made to make things easier there is then an opportunity
  • Interface change – changing the design of something radically can help find new opportunities, for example the endless scrolling radically changed design in many areas where Pinterest and Instagram grew

Case studies of note

The Bible app is one of the most successful apps and a key feature it has is reading plans. These are verses grouped by theme, which break down the Bible into more manageable chunks, thus making consumption and habit easier.

It also tackled hooked model 4 of investment, by noting what the user had already read. Investment is also present in developing a streak much like Duolingo does.

Variability is also present with different plans; verses are surfaced as suggestions for the user. However, Gruenewald, the founder, does note that they must be mindful of what is interpreted as ‘from God’.

Finally, investment is captured again by way of bookmarks and highlighting.

This is an app that tracks your weights, reps and sets. As such, the reward of self is hit, as is the variability of what you can fit in your next rep and set.

Last thoughts

Nir Eyal, the author, gives some compelling and scientific reasoning to human behaviour but highlights the moral implication of our work as product people – and I mean that to include anyone that makes anything.

Ps. A quote I keep thinking about from the book.

A business’ value is a sum of its future profits.

Focused on saving our time: for your life balance; for our food emissions and for booking airbnbs.