Jonathan Haidt argues that two shifts, arriving together, explain the sharp rise in teen anxiety and depression that began around 2010. Children got less freedom in the physical world, as parents cut back the unsupervised play and risk-taking earlier generations relied on to build competence and confidence. At the same time, they got a smartphone and, through it, unrestricted access to social media, at exactly the age when peer approval matters most.
Haidt calls the years 2010 to 2015 the Great Rewiring: front-facing cameras, the first iPad, unlimited data plans and the "like" button all arrive in a short window, and indicators of teen mental health bend upward across several countries at nearly the same time. He traces four ways a phone-based childhood displaces a play-based one: it cuts sleep, replaces in-person time with friends, fragments attention with constant notifications, and produces a compulsive, hard-to-quit relationship with the device itself.
The harms land differently by sex. Girls, whose social conflict runs more through exclusion, gossip and appearance, are more exposed on platforms built around images and comparison. Boys, pushed out of a real world that has grown less tolerant of roughhousing and risk, retreat instead into gaming and video, chasing the sense of mastery and competition they are no longer allowed to find outside.
Haidt proposes four norms rather than rules, because a family that opts out alone only isolates its own child: no smartphone before high school, no social media before sixteen, phone-free schools, and far more unsupervised play. He closes by acknowledging real pushback: researchers including Candice Odgers have argued the evidence for a causal link is weaker than the book presents, and that the mental health decline is real even if its cause is not settled.