The mystery of addiction — what it is, what causes it and how to end it — threads through most of our lives. Experts estimate that one in 10 Americans is dependent on alcohol and other drugs, and if we concede that behaviors like gambling, overeating and playing video games can be addictive in similar ways, it’s likely that everyone has a relative or friend who’s hooked on some form of fun to a destructive degree. But what exactly is wrong with them? For several decades now, it’s been a commonplace to say that addicts have a disease. However, the very same scientists who once seemed to back up that claim have begun tearing it down.