Hooked: How to Build Habit-Forming Products

In Hooked, Nir Eyal explores the relationship between human psychology and product design. He argues that the most successful products are those that cater to intrinsic human needs, instincts, and biases. Throughout his work, Eyal refers to scientific studies which reveal different phenomena in human psychology, and how these aspects of cognition can be successfully exploited by advertising or product design.

For instance, Eyal describes how in 1975, researchers investigated how the quantity of an item influenced people’s perception of its worth. They found that people tended to value scarce items as more valuable than those which were plentiful. He explains: “The appearance of scarcity affected their perception of value […] The group left with only two cookies rated them to be more valuable, while those experiencing sudden abundance by going from two to ten actually valued the cookies less” (85).

Eyal refers to this as the “scarcity effect.” He argues that this heuristic is also highly relevant to people’s online behavior. Online shopping sites often employ a tactic that depends on the scarcity effect: They announce that there are few items left in stock, thereby making that product seem more appealing and valuable to the consumer. Eyal uses his own experience of shopping on Amazon as an example of this tactic at work. He writes:

For an example of how perception of a limited supply can increase sales, look no further than Amazon.com. My recent search for a DVD revealed that there were ‘only 14 left in stock,’ while a search for a book I’ve had my eye on says only three copies remain. Is the world’s largest online retailer almost sold out of nearly everything I want to buy or are they using the scarcity heuristic to influence my buying behavior? (86).

Eyal cites a French study which showed that people who are reminded of their freedom to make their own choices are actually more easily persuaded to perform a certain task, such as giving money to a stranger. Eyal uses this information to argue that by acknowledging the user’s autonomy, and incorporating designs which emphasize user freedoms, products can reduce people’s “reactance,” or rebellion against feeling controlled (121). He points to his own experiences using fitness apps to demonstrate this heuristic at work. He explains that one app’s strict approach triggered his reactance, which prompted him to abandon it altogether: “I soon felt obligated to confess my mealtime transgressions to my phone […] My only options were to comply or quit; I chose the latter” (122). In contrast, an app which had more flexibility in its design and quickly rewarded Eyal with social validation successfully hooked him. He recalls: “Before my reactance alarm went off I started receiving kudos from other members of the site after entering my very first run […] I have not used Fitocracy for long, but it is easy to see how someone could get hooked” (122).

Eyal also investigates the “endowed progress effect,” a cognitive bias which motivates people to complete tasks that they have started in order to feel a sense of accomplishment and closure (89). Eyal cites a study which demonstrated that when customers are given punch cards with free “punches” they are 82% more likely to continue revisiting the service and complete their punch card (90). Eyal claims that video games, Facebook, and LinkedIn all successfully exploit this strategy by providing users with a measurement of their “progress” in a game or profile creation and nudging them to complete certain tasks and reach their “final goal” (90).

By explaining the science behind each heuristic and then providing real-life examples of each one at work in advertising or product design, Eyal aims to show the reader that these biases are real and that they can profit from them, too. He claims: “For product designers building habit-forming technology, understanding and leveraging these methods for boosting motivation and ability can prove highly impactful” (91).