A staggering 129 million Americans have at least one major chronic disease—and 90% of our $4.1 trillion in annual health care spending goes toward treating these physical and mental-health conditions. That financial and personal toll is only projected to grow.We know this is unsustainable. But there are solutions, because health outcomes are shaped by more than just medical care or genes. Behavior change can be a miracle drug, both for preventing disease and for optimizing the treatment of disea...