According to Jon Grant at University of Chicago Medicine, all things that give us an excessive reward—like excessive happiness (euphoria) or comfort—are addictive. Not just taking drugs, but eating particular foods, shopping, having sex, shoplifting, using social media—all these actions have an addictive nature. Put simply, the reason why I run is that it feels good, and you could say that I’m addicted to it.
People develop a fondness for things that are easy to do and offer rewards, and can quickly make them a habit.