Kaptein and his colleagues tested a personalized, adaptive approach to persuasion that relies on combining these three elements in optimal fashion. To test their ability to persuade, they recruited a sample of Dutch adults who agreed to have their snacking habits tracked on their cellphones. You may use a similar app to track your movement and sleep patterns. Every once in a while, it sends you a message intended either to reward you for reaching a goal (such as walking so many steps) or to encourage you to do something differently that will promote healthier habits (such as getting more sleep). The messages these apps send are not particularly personalized to you, other than to send particular reminders or rewards depending on the behavior it tracks. They do not factor in your personality, or what sorts of messages will likely affect you.