Book review: “Hooked: how to build habit-forming products”

What makes a product or service really stick in your mind? Do you have an app on your phone that you always turn to whenever you’re bored? If you’ve got a problem to solve, is there a specific product or service you tend to use to look for a solution? American journalist and lecturer Nir Eyal has written a book about how to best create ‘habit-forming’ products, creating ways for users to get ‘hooked’. In “Hooked: how to build habit-forming products” Nir focuses on those elements that make up the “Hook Model” and which help to create products which become an integral part of our lives.

What I liked best about reading “Hooked” are the insights that it provides around the user journey that product people can design and optimise for; not just designing for a one-off experience but creating a lasting engagement with the user. Nir illustrates this form of lasting engagement through the so-called “Habit Zone” which plots ‘frequency’ against ‘perceived utility’ (see Fig. 1 below). Let’s start this review by looking at the four elements of the Hook Model: Trigger, Action, Variable Reward and Investment (also see Fig. 2 below):

  1. Trigger  Nir describes a trigger as “the actuator of behaviour – the spark plug in the engine.” There are two forms of triggers: external and internal triggers. Habit-forming products use external triggers such as as an email or a website link to alert users. These are all external alerts. The point that Nir makes is that when users start to automatically cue their next behaviour, the new habit becomes part of their everyday routine. In other words: as soon as users no longer need an external alert, a habit – powered internally – has been formed.
  2. Action – A trigger is pretty useless if it isn’t followed by an action. Nir explains that “to initiate action, doing must be easier than thinking” and refers to the “Fogg Behaviour Model” in this respect (see Fig. 4 below). This model shows that behaviour will occur when motivation, ability, and a trigger occur at same time and in sufficient measures. I found it particularly interesting to read about ‘ability’ and BJ Fogg’s six “elements of simplicity”, which represent the factors that influence the difficulty of a specific action (see Fig. 5 below). This focus on making actions as easy as possible is one of the key reasons why companies are moving towards ‘single purpose’ apps and are constantly looking to reduce the number of steps that users have to go through (I wrote about single purpose apps a few weeks ago). Nir also asks the question around where to start: motivation or ability? His answer is very clear: always start with ability. Nir’s point here is that “for most companies building technology solutions, the greatest return on investment will generally come from increasing a product’s ease-of-use.”
  3. Variable Reward – The word that intrigued me most with regard to this third element of the Hook model was “variable”. In the book, Nir explains that when users are (pleasantly) surprised by a new reward, this is likely to have an impact on their usage of the product or service. Three different types of variable rewards are further explained in the book: the “Tribe”, the “Hunt” and the “Self” (see Fig. 6 below). Habit-forming products tend to use one or more of these variable reward types in order to keep users excited and engaged.
  4. Investment – The fourth and final element of the Hook model is “investment” This is about getting users to invest, to put effort into a product. Nir talks about a psychological phenomenon known as the “escalation of commitment” whereby people are driven to keep on investing into a product or service. It’s a phenomenon often encountered in video games, where players go through countless levels of a game. Twitch is a great example of a successful community built around some of these characteristics. The key point here is that the more users invest time and effort into a product or service, the more they value it. Nir talks about “storing value” in this regard; the stored value users put into the product increases the likelihood they will use it again in the future and comes in a variety of forms (see Fig. 7 below).

In Chapter 6 of the book, Nir provides a nice overview of the five fundamental questions for building fundamental hooks (see Fig. 8 below). He goes on to explain that the Hook Model is fundamentally about changing people’s behaviours; but the power to build persuasive products should be used with caution. He acknowledges that the Hook Model and subsequent persuasive products can be abused by product people and introduces the “Manipulation Matrix” in this regard (see Fig. 9 below).

There were a few more key things which I took away from reading “Hooked: how to build habit forming products”:

  1. Avoid manipulation – As a product person, the role of a “Facilitator” is the one that you want to play; creating a product that you would use and that you believe will make the user’s life better. In effect, you’re facilitating a healthy habit. I guess that’s exactly the main concern that I have with some product people and their application of some of the insights and examples in “Hooked”. I hear people talking about ‘tricks’ and ‘mechanisms’ and I worry sometimes that the underlying user need gets overlooked or downplayed. It’s one of the reasons why I believe that product people should always take the Internal Trigger as a key reference point when creating and evaluating a product or a service.
  2. Habit Testing – Inspired by the build-measure-learn approach of the “Lean Startup” movement, Nir introduces the continual process of “Habit Testing” which can help offer insights and actionable data to inform the design of habit-forming products. The practical steps that Nir outlines with regard to Habit Testing are very useful and can easily be integrated in one’s more standard user testing processes (see Fig. 10 below).

Main learning point: In “Hooked: how to build habit-forming products” Nir Eyal provides a very useful lens for anyone involved in product development. User habits are pivotal and the “Habit Zone” is where most products and services will want to be. The aspects of the Hook Model which I found most helpful are Trigger and Action as both got me to think more about what drives users and how to best translate this motivation into action. If you are interested in learning more about how user habits are formed and how products can tap into this, then “Hooked” is a must-read!


Fig. 1 – The Habit Zone by Nir Eyal (taken from: habit-zone2

Fig. 2 – The Hook Model by Nir Eyal (taken from: Hook Model

Fig. 3 – Types of external and internal triggers (taken from: “Hooked: how to create habit-forming products” by Nir Eyal, Chapter 2):

External triggers:

  1. Paid Triggers – Advertising, search engine marketing, and other paid channels are commonly used to get users’ attention and prompt them to act.
  2. Earned Triggers – Earned triggers are free in that they can not be bought directly, but they often require investment in the form of time spent on public and media relations.
  3. Relationship Triggers – One person telling others about a product or a service can be a highly effective external trigger for action.
  4. Owned Triggers – Owned triggers consume a piece of real-estate in the user’s environment. They consistently show up in daily life and it is ultimately up to the user to opt into allowing these triggers to appear. Owned triggers are only set after users sign up for an account, submit their email address, install an app, opt into newsletters, or otherwise indicate that they want to continue receiving communications.

Internal Triggers: 

  1. Emotional Triggers – Emotions, particularly negative ones, are powerful internal triggers and greatly influence our daily routines. Feelings of boredom, loneliness, frustration, confusion and indecisiveness often instigate a  slight pain or irritation and prompt an almost instantaneous and mindless action to quell the negative sensation. Positive emotions can also serve as internal triggers, and may even be triggered themselves by a need to satisfy something that is bothering us.


Fig. 4 – BJ Fogg’s Behaviour Model (taken from: Behavior Model

Fig. 5 – BJ Fogg’s six “elements of simplicity” (taken from: “Hooked: how to create habit-forming products” by Nir Eyal, Chapter 3)

  • Time – How long it takes to complete an action.
  • Money – The fiscal cost of taking an action.
  • Physical Effort – The amount of labour involved in taking the action.
  • Brain Cycles  The level of mental effort and focus required to take an action.
  • Social Deviance – How accepted the behaviour is by others.
  • Non-Routine – How much the action matches or disrupts existing routines.


Fig. 6 – Three Variable Reward Types (taken from: “Hooked: how to create habit-forming products” by Nir Eyal, Chapter 4)

  • Rewards of the Tribe – Rewards which are based on the way in which our brains are adapted to seek rewards that make us feel accepted, attractive, important, and included. Examples of such rewards can be found in sites such as Quora and Stack Overflow.
  • Rewards of the Hunt – This reward type is very much about the ‘chase’; the pleasure we can derive from the pursuit itself. A good example is Pinterest where users never know what they will find on the site. To keep users searching and scrolling, some of the pictures on Pinterest seem to be cut off. However, the idea is for these images to ‘tease’ the user and to offer them a glimpse of what’s ahead.
  • Rewards of the Self – This third and final variable reward type has to do with a more personal form of gratification. Nir mentions a good example in video games, where players seek to master the skills needed to pursue their quest. A good example can be found in Twitch which has built a great community around some of these characteristics.


Fig. 7 – Types of investment, storing value into products or services (taken from: “Hooked: how to create habit-forming products” by Nir Eyal, Chapter 5)

  • Content – Examples of sites where users store value by adding content are Spotify (where users create, store and share music playlists) and photo-sharing site Flickr. Similarly, users can store value through content in the form of “likes” or videos shared on Facebook.
  • Data – Users can store value in a product or service by adding data about themselves or their behaviours. Good examples are LinkedIn (where people store their CVs and keep details of their business contacts) and Tripit (where people create and store their travel itineraries).
  • Followers – Apart from the gratification that people can get from having a large number of followers on social media such as Twitter and Quora, Nir argues that the more followers one has, the more valuable the service becomes to the user as a result.
  • Reputation – Reputation as a form of stored value comes in all kinds of different shapes and sizes. Nir mentions online marketplaces such as eBay and Airbnb where people with negative scores are treated very differently from those with good reputations.
  • Skill – Investing time and effort into learning to use a product is a form of investment and stored value. Once a user has acquired a skill, the service becomes easier and moves users to the right on the ability Axis of the Fogg Behaviour Model (see Fig. 4 above). A good example is the well known graphics editing programme Adobe Photoshop which enables users to pick from a wide range of features, varying from basic to very advanced.


Fig. 8 – Five fundamental questions for building effective hooks (taken from: “Hooked: how to create habit-forming products” by Nir Eyal, Chapter 6)

  1. What do users really want? What pain is your product relieving? (Internal Trigger)
  2. What brings users to your service? (External Trigger)
  3. What is the simplest action users take in anticipation of reward, and how can you simplify your product to make this action easier? (Action)
  4. Are users fulfilled by the reward, yet left wanting more? (Variable Reward)
  5. What “bit of work” do users invest in your product? Does it load the next trigger and store value to improve the product with use? (Investment)


Fig. 9 – Manipulation Matrix (taken from:


Fig. 10 – Steps involved in Habit Testing (taken from: “Hooked: how to create habit-forming products” by Nir Eyal, Chapter 8 and

  • Step 1: Identify – Define what it means to be a devoted user. How often “should” one use your product?
  • Step 2: Codify – Codify the steps that your users took using your product to understand what hooked them. You’re looking for a “Habit Path”; a series of similar actions shared by your most loyal users.
  • Step 3: Modify – Armed with new insights, it’s time to revisit your product and identify ways to nudge new users down the same Habit Path as taken by devotees.

Screen Shot 2012-04-05 at 11.17.20 AM


Related links for further learning:






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