What separates Hooks from a plain vanilla feedback loop is their ability to create wanting in the user. Feedback loops are all around us, but predictable ones don’t create desire. The predictable response of your fridge light turning on when you open the door doesn’t drive you to keep opening it again and again. However, add some variability to the mix—say a different treat magically appears in your fridge every time you open it—and voila, intrigue is created. You’ll be opening that door like a lab animal in a Skinner box.

Variable schedules of reward are one of the most powerful tools that companies use to hook users. Research shows that levels of dopamine surge when the brain is expecting a reward. Introducing variability multiplies the effect, creating a frenzied hunting state, activating the parts associated with wanting and desire. Although classic examples include slot machines and lotteries, variable rewards are prevalent in habit-forming technologies as well.

When Barbra lands on Pinterest, not only does she see the image she intended to find, but she’s also served a multitude of other glittering objects. The images are associated with what she’s generally interested in – namely things to see during a trip to rural Pennsylvania – but there are some others that catch her eye also. The exciting juxtaposition of relevant and irrelevant, tantalizing and plain, beautiful and common sets her brain’s dopamine system aflutter with the promise of reward. Now she’s spending more time on the site, hunting for the next wonderful thing to find. Before she knows it, she’s spent 45 minutes scrolling in search of her next hit.