"After more than a decade of stability or improvement, the mental health of adolescents plunged in the early 2010s. Rates of depression, anxiety, self-harm, and suicide rose sharply, more than doubling on most measures. Why? In [this book], social psychologist Jonathan Haidt lays out the facts about the epidemic of teen mental illness that hit many countries at the same time. He then investigates the nature of childhood, including why children need...