“Because the brain grades on a curve, endlessly comparing the present with what came just before, the secret to happiness may be unhappiness. Not unmitigated unhappiness, of course, but the transient chill that lets us feel warmth, the sensation of hunger that makes satiety so welcome, the period of near-despair that catapults us into the astonishing experience of triumph.” Neurobiologist Indira M. Raman explains why the brain requires that contrast.