100 Things Every Designer Needs to Know About People, 2nd Edition

53 Unpredictability Keeps People Searching

Dopamine is also stimulated by unpredictability. When something happens that is not exactly predictable, it stimulates the dopamine system. Think about electronic devices. Emails and tweets and texts show up, but you don’t know exactly when they will arrive or who they will be from. It’s unpredictable. This is exactly what stimulates the dopamine system. It’s the same system at work for gambling and slot machines. Basically, email, Twitter, and most social media run on the variable-ratio schedule discussed earlier in this chapter. That makes it likely that people will engage in the behavior again and again.

The Pavlovian Reflex

The dopamine system is especially sensitive to cues that a reward is coming. ...