Why it is impossible for some to 'just say no'

Drug abuse, crime and obesity are but a few of the problems our nation faces, but they all have one thing in common—people’s failure to control their behavior in the face of temptation. While the ability to control and restrain our impulses is one of the defining features of the human animal, its failure is one of the central problems of human society. So, why do we so often lack this crucial ability"