"At the age of 36, on the verge of a completing a decade's worth of training as a neurosurgeon, Paul Kalanithi's health began to falter. He started losing weight and was wracked by waves of excruciating back pain. A CT scan confirmed what Paul, deep down, had suspected: he had stage four lung cancer, widely disseminated. One day, he was a doctor making a living treating the dying, and the next, he was a patient struggling to live. Just like that,...