Proposed by Nir Eyal and Ryan Hoover, it consists of four elements: trigger, action, reward, and investment.
A trigger entices people to take action; an action drives people to obtain a reward; a reward keeps people motivated to continue taking action.
Investment means that continued action consumes a great deal of money and energy, making it difficult for people to break away.
The model was originally designed for marketing as a continuous cycle of behaviors that would get users hooked on a product without them realizing it, turning them into loyal customers. Outside marketing, the causes of various human addictions can also be found in this model. The reason the HOOK model can serve as a hook is that each of its four elements has a hook behind it.
The hook behind a trigger is desire; the hook behind action is simplicity; the hook behind reward is luck; and the hook behind investment is wealth.
Trigger: human desire. Whether the trigger is internal or external, as long as a person is not being coerced, it is their own desire that draws them through the gateway to addiction. Videos that resonate with people and ads that hit their pain points can both prompt them to act of their own accord. Liking or placing an order happens because you reminded them of what they themselves want.
Action: If a behavior is too difficult or takes too long, it will inevitably become a barrier to addiction, because only simplicity enables mindless repetition of an action, and repetition is the foundation of addiction.
Rewards. If something relies entirely on skill and not at all on luck, it will hold no surprises. If rewards are highly consistent or predictable, they will be utterly boring. The key to addiction is luck: luck makes rewards random, allowing them to be high or low and making them uncertain—and it is uncertainty that fills people with anticipation for each next time. The earliest addictive sunflower seeds were designed with one end heavily flavored and the other lightly flavored, making some feel delicious and others merely average, so you keep eating without stopping. The same goes for playing cards: luck can be good or bad, and you do not know what your hand will be like next round, but you look forward to it and keep playing. Stimulation, no matter how intense, will tend toward blandness if it is consistent. Contributions, no matter how large, will come to be taken for granted if they are consistent; only random uncertainty can stir people's emotions. When you are filled with anticipation for the next time, addiction is formed.
Investment. What makes it so hard for us to break away is not the energy and money we put in, but the wealth we acquire with them. The top-tier gear you draw, the honor rankings you achieve, and the social networks you build are all your wealth. They are what make it hard for you to let go and impossible to pull yourself away—not money. Big bro spends 648 every day; isn't there any sunk cost? No fun—he can quit just like that. But when one of the underlings in the guild you organized gets bullied, that's not okay. Big bro has to log in. Oh, and there are comeback rewards and new gameplay features—the hooks in the trigger sequence have worked on big bro again.
Desire, simplicity, luck, and wealth are the hooks of the addiction model. But the deeper question is: why do these become hooks? Because each of these hooks can draw out one of the original sins. Too much desire can draw out delusion. If you can always accurately tell me what I want and what I should want, I will want more and more, until I lose all sense of timing. Too much simplicity can draw out laziness. If I only need to open my mouth and move my hands to get unprecedented satisfaction, who would still be willing to take the so-called long way around? Too much luck can draw out greed. I just need one more try, one more try, and next time it will surely work. Too much wealth can draw out obsession. I believe that illusory happiness is still happiness; guarding that illusory beauty can cover up the real predicament. Delusion, laziness, greed, and obsession are like the Four Horsemen of the Apocalypse of the human mind—once they appear, they drag people into hidden abysses. Delusion is the sharp blade that gets you in the door; laziness is the routine of mindless repetition; greed is the gravity of 'one more time'; obsession is the resistance to turning back and coming ashore. These four can leave a person unable to move—once you're caught, how easy can it be to break free? People often ask me whether there is a way to deal with addiction. I thought about it for a long time without an answer, and later I realized that having no answer seems to be the answer itself. If there were an easy way to deal with it, it wouldn't deserve to be called addiction. So the best place to deal with addiction is not within the addiction itself, but before it takes hold. When you find that something meets the conditions of the addiction model and has hooks, then while the addiction has not yet formed, don't continue.