Sendhil Mullainathan: Solving social problems with a nudge

MacArthur winner Sendhil Mullainathan uses the lens of behavioral economics to study a tricky set of social problems — those we know how to solve, but don’t. We know how to reduce child deaths due to diarrhea, how to prevent diabetes-related blindness and how to implement solar-cell technology … yet somehow, we don’t or can’t. Why?