"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 play and independent exploration to mature into competent, thriving adults. Haidt shows how the play-based childhood began to decline in the 1980s, and how it was finally wiped out by the arrival of the phone-based childhood in the early 2010s. ... Most important, Haidt issues a clear call to action. He diagnoses the collective action problems that trap us, and then proposes four simple rules that might set us free."