Looking at what today’s successful tech companies like Facebook, Twitter and Pinterest all have in common, one thing is clear. These companies all influence, if not create, user habits. 

Figuring out exactly how they do that is habit design researcher Nir Eyal’s job. Eyal spoke Wednesday to a crowd of about 70 people in San Francisco about the psychology behind habit-forming technologies. The event was hosted by Tradecraft, a local organization that puts on talks and workshops for UX, UI, and growth and sales professionals.

Eyal has taught "Using Neuroscience to Influence Human Behavior" at the Stanford Graduate School of Business and now consults companies and writes about the intersection of human psychology and tech.

“Facebook and Twitter couldn’t exist if you didn’t use them out of habit. If they had to send you a message every time, it wouldn’t work. Those types of businesses require what I call ‘unprompted user engagement,’” Eyal said. 

Why are their products so highly engaging, and borderline addictive? Eyal started noticing patterns amongst successful companies, and he used his observations to form a four-part framework. It’s what he calls the Hook Model, and it involves: 

A trigger. A trigger is some kind of call to action like an email, or a piece of information that tells you what to do next. 

An action. This is a simple behavior that a user performs in anticipation of a reward. For example, scrolling on Twitter. Eyal said the act of scrolling stimulates the brain similar to the way that pulling a slot machine does. 

The reward. The reward is variable. On Twitter, for example, users are always looking for the next most interesting post, and this will be different each time. 

The investment. This involves getting the user to put something back into the product. It’s the phase the most startups neglect, according to Eyal. 

“If you don’t get the user to put something of value into the system, you’re missing a huge opportunity,” he said.

In the case of Instagram, the company has its users building up their online albums every time they post a picture. And the more content there is on Instagram, the better it gets. Eyal said that technology differs from physical objects in a very specific way. 

“Your phones, tables and chairs, these things depreciate. They lose value with time. But habit-forming technology has the opportunity to appreciate,” Eyal said. “It should get better the more you use it.”