Susan Cain urged our society to cultivate space for the undervalued, indispensable introverts among us, thereby revealing an untapped power hidden in plain sight. Now, she employs the same mix of research, storytelling, and memoir to explore why we experience sorrow and longing, and the surprising lessons these states of mind teach us about creativity, compassion, leadership, spirituality, mortality and love. Bittersweetness is a tendency to states of longing, poignancy, and sorrow; an acute awareness of passing time; and a curiously piercing joy when beholding beauty. But bittersweetness is not, as we tend to think, just a momentary feeling or event. It's also a way of being, a storied heritage. Our artistic and spiritual traditions - amplified by recent scientific and management research - teach us its power.