Nir Eyal explains in the book about all forms of products have hooks in them such as "apps, sports, movies, games and even our jobs". It's said that, "Hooks can be found in virtually any experience that burrows into our minds (and often our wallets).
The process in which the consumers get hooked is based on 'The Hook Model' which consists of the four phases; trigger, action, variable reward and investment.
The trigger is the start of the consumer's behaviour and there are two types of triggers known as the internal and external. An example would be through using external triggers such as "an e-mail, a Website link, or the app icon on a phone". An example for an internal trigger is the use of Facebook. The consumer may use the social app at first just to view what their friends are doing and what they have done but it gradually becomes used more and more often thus it's slowly becoming a habit and being used in their everyday routine in life.
The action is "the behaviour done in anticipation of a reward" which is typically a simple action carried out by the user in order to receive a particular reward. For example, clicking a picture on Facebook which will lead to the picture enlarging itself and allowing the user to see the picture closely with better quality.
The variable reward is said to be "one of the most powerful tools companies implement to hook users". The hook's ability is to create a craving for users to repeat their actions but with another reward applying to that same action, this creates a sense of intrigue for the user.
The investment stage involves the user doing some work which is an increase in the likelihood of the user repeating the cycle of the 'Hook model' in the future. This requires the user to "put something into the product or service such as time, data, effort, social capital, or money". This stage implies an action that helps better the product or service in order for the next time it's used. It also engages the user with the product by showing their commitment to the good or service by mentioning it to their friends and family. "These commitments can be leveraged to make the trigger more engaging, the action easier, and the reward more exciting with every pass through the Hook cycle."
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Bibliography
Eyal, N. (no date) Hooked: How to Build Habit-Forming Products. United Kingdom: Portfolio Penguin.
Citation
(Eyal, no date, pp. 6 – 10)