Nir Eyal
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Not only did this book open my eyes to the methods used by product designers to engage and addict users, but it also proved incredibly useful in kicking my smartphone addiction.
  • Habit — “automatic behaviours triggered by situational cues”: things we do with little or no conscious thought.
  • Trigger — actuator of behaviour—the spark plug in the engine. Triggers come in two types: external and internal.
  • Action — the behaviour done in anticipation of a reward. Companies leverage two basic pulleys of human behaviour to increase the likelihood of an action occurring: the ease of performing an action and the psychological motivation to do it.
  • Variable reward — variability of the reward which creates a desire for feedback, motivating the user to seek it out. Research shows that levels of the neurotransmitter dopamine surge when the brain is expecting a reward.
  • Investment — occurs when the user puts something into the product of service such as time, data, effort, social capital, or money. Increases the odds that the user will make another pass through the Hook cycle in the future.

The Habit Zone

Fostering consumer habits is an effective way to increase the value of a company by driving higher customer lifetime value (CLTV): the amount of money made from a customer before that person switches to a competitor, stops using the product, or dies.

Facebook’s success was, in part, a result of what I call the more is more principle—more frequent usage drives more viral growth.

Altering behaviour requires not only an understanding of how to persuade people to act but also necessitates getting them to repeat behaviours for long periods, ideally for the rest of their lives.

The enemy of forming new habits is past behaviours, and research suggests that old habits die hard. Even when we change our routines, neural pathways remain etched in our brains, ready to be reactivated when we lose focus. Research shows that nearly everyone who loses weight on a diet gains back the pounds within two years. In order for an infrequent action to become a habit, the user must perceive a high degree of utility, either from gaining pleasure or avoiding pain.

A company can begin to determine its product’s habit-forming potential by plotting two factors: frequency (how often the behaviour occurs) and perceived utility (how useful and rewarding the behaviour is in the user’s mind over alternative solutions).

Some habits can take form in a matter of weeks, while others can take up to five months.

Vitamins or painkillers? - a common question asked by investors. Thew correct answer, from the perspective of most investors, is the latter: a painkiller. Gatekeepers such as investors and managers want to invest in solving real problems or meeting immediate needs by backing painkillers. Recent evidence actually shows taking multivitamins may actually be doing more harm than good.

Habit-forming technologies are both vitamins and painkillers.

These services seem at first to be offering nice-to-have vitamins, but once the habit is established, they provide an ongoing pain remedy. Although some people use the terms interchangeably, habits are not the same things as addictions. The latter word means persistent, compulsive dependencies on a behaviour or substance.

Habits cannot form outside the Habit Zone, where the behaviour occurs with enough frequency and perceived utility.

Habit-forming products often start as nice-to-haves (vitamins) but once the habit is formed, they become must-haves (painkillers).

Habit-forming products alleviate users’ pain by relieving a pronounced itch. Designing habit-forming products is a form of manipulation.

Key Question — What problem are users turning to your product to solve?


Triggers cue the user to take action and provide the basis for sustained behaviour change. Advertising, search engine marketing, and other paid channels are commonly used to get users’ attention and prompt them to act. Favourable press mentions, hot viral videos, and featured app store placements are all effective ways to gain attention. One person telling others about a product or service can be a highly effective external trigger for action.

When designers intentionally trick users into inviting friends or blasting a message to their social networks, they may see some initial growth, but it comes at the expense of users’ goodwill and trust.

Triggers come in two types—external and internal. Internal triggers tell the user what to do next through associations stored in the user’s memory - they manifest automatically in the users mind. External triggers tell the user what to do next by placing information within the user’s environment. Connecting internal triggers with a product is the brass ring of consumer technology. Emotions, particularly negative ones, are powerful internal triggers and greatly influence our daily routines. Once a technology has created an association in users’ minds that the product is the solution of choice, they return on their own, no longer needing prompts from external triggers.

A study demonstrated that people suffering from symptoms of depression used the Internet more.

To build a habit-forming product, makers need to understand which user emotions may be tied to internal triggers and know how to leverage external triggers to drive the user to action. The ultimate goal of a habit-forming product is to solve the user’s pain by creating an association so that the user identifies the company’s product or service as the source of relief.

You’ll often find that people’s declared preferences—what they say they want—are far different from their revealed preferences—what they actually do.

Notable tools to understand user narratives: customer development, usability studies, 5 why’s method and empathy maps.

Key Question — How can you couple an external trigger as closely as possible to when the user’s internal trigger fires?


The action is the simplest behaviour in anticipation of reward. The more effort—either physical or mental—required to perform the desired action, the less likely it is to occur.

Dr. B. J. Fogg’s Behaviour Model: - For any behaviour to occur, a trigger must be present at the same time as the user has sufficient ability and motivation to take action. To increase the desired behavior, ensure a clear trigger is present; next, increase ability by making the action easier to do; finally, align with the right motivator. Every behavior is driven by one of three Core Motivators: seeking pleasure and avoiding pain; seeking hope and avoiding fear; seeking social acceptance while avoiding social rejection. Ability is influenced by the six factors of time, money, physical effort, brain cycles, social deviance, and non-routineness. Ability is dependent on users and their context at that moment.

The action phase of the Hook Model incorporates Fogg’s six elements of simplicity by asking designers to consider how their technology can facilitate the simplest actions in anticipation of reward.

Motivation vs ability - where is your time and money better spent? The answer is always to start with ability. Influencing behaviour by reducing the effort required to perform an action is more effective than increasing someone’s desire to do it.

Heuristics are cognitive shortcuts we take to make quick decisions. Product designers can utilise many of the hundreds of heuristics to increase the likelihood of their desired action. There are many counterintuitive and surprising ways companies can boost users’ motivation or increase their ability by understanding heuristics.

Scarcity effect - a product can decrease in perceived value if it starts off as scarce and becomes abundant. Framing effect - the mind takes shortcuts informed by our surroundings to make quick and sometimes erroneous judgments. Anchoring effect - people often anchor to one piece of information when making a decision. Endowed progress effect, a phenomenon that increases motivation as people believe they are nearing a goal.

Key Questions

  • Which resources are limiting your users’ ability to accomplish the tasks that will become habits?
  • Time, Brain cycles (too confusing), Money, Social deviance (outside the norm), Physical effort, Non-routine (too new)

Variable Reward

Stanford professor Brian Knutson found that 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. To hold our attention, products must have an ongoing degree of novelty.

Three types of variable rewards: the tribe, the hunt, and the self.

Rewards of the tribe is the search for social rewards fuelled by connectedness with other people. Our brains are adapted to seek rewards that make us feel accepted, attractive, important, and included.Sites that leverage tribal rewards benefit from what psychologist Albert Bandura called “social learning theory.

Rewards of the hunt is the search for material resources and information. The need to acquire physical objects, such as food and other supplies that aid our survival, is part of our brain’s operating system.

Rewards of the self is the search for intrinsic rewards of mastery, competence, and completion. As highlighted by the work of Edward Deci and Richard Ryan. Their self-determination theory espouses that people desire, among other things, to gain a sense of competency. Adding an element of mystery to this goal makes the pursuit all the more enticing.

Only by understanding what truly matters to users can a company correctly match the right variable reward to their intended behaviour. When there is a mismatch between the customer’s problem and the company’s assumed solution, no amount of gamification will help spur engagement. Rewards must fit into the narrative of why the product is used and align with the user’s internal triggers and motivations.

When our autonomy is threatened, we feel constrained by our lack of choices and often rebel against doing a new behaviour. Psychologists refer to this as reactance. Maintaining a sense of user autonomy is a requirement for repeat engagement.

A recent study found social factors were the most important reasons people used the service and recommended it to others

Experiences with finite variability become increasingly predictable with use and lose their appeal over time. Experiences that maintain user interest by sustaining variability with use exhibit infinite variability.

Variable rewards must satisfy users’ needs while leaving them wanting to reengage with the product.


Unlike the action phase, which delivers immediate gratification, the investment phase concerns the anticipation of rewards in the future.

A psychological phenomenon known as the escalation of commitment has been shown to make our brains do all sorts of funny things. The more users invest time and effort into a product or service, the more they value it. In fact, there is ample evidence to suggest that our labor leads to love.

We irrationally value our efforts - IKEA example, there’s a hidden benefit to making users invest physical effort in assembling their products—by asking customers to assemble their own furniture,  they adopt an irrational love of the furniture they built.

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. LinkedIn found that the more information users invested in their site, the more committed they became to it.

Investments in a product create preferences because of our tendency to overvalue our work, be consistent with past behaviours, and avoid cognitive dissonance.

Investment comes after the variable reward phase, when users are primed to reciprocate.

Investments increase the likelihood of users returning by improving the service the more it is used. They enable the accrual of stored value in the form of content, data, followers, reputation, or skill.

Investments increase the likelihood of users passing through the Hook again by loading the next trigger to start the cycle all over again

What Now?

Five fundamental questions for building effective hooks:

  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)
To help you, as a designer of habit-forming technology, assess the morality behind how you manipulate users, it is helpful to determine which of the four categories your work fits into. Are you a facilitator, peddler, entertainer, or dealer?

Facilitators use their own product and believe it can materially improve people’s lives. They have the highest chance of success because they most closely understand the needs of their users.

Peddlers believe their product can materially improve people’s lives but do not use it themselves. They must beware of the hubris and inauthenticity that comes from building solutions for people they do not understand firsthand.

Entertainers use their product but do not believe it can improve people’s lives. They can be successful, but without making the lives of others better in some way, the entertainer’s products often lack staying power.”

Dealers neither use the product nor believe it can improve people’s lives. They have the lowest chance of finding long-term success and often find themselves in morally precarious positions.

Image credits: Hooked by Nir Eyal