The mechanism through which new technologies cause developmental harm — not by direct damage but by offering easier alternatives to the experiences through which psychological capacity is built, which the brain's energy-conservation bias reliably prefers.
Displaced developmental experience is the central causal mechanism in Twenge's framework. The claim is not that technology damages developing brains directly but that technology offers alternatives that are easier, faster, and more immediately rewarding than the experiences through which developmental capacity is historically built — and that the brain, operating as an energy-conservation machine, reliably chooses the easier alternative. The effect operates invisibly because what is displaced leaves no evidence of its absence: the teenager who spends three hours scrolling instead of three hours building something has not produced a measurable deficit on any standard assessment, but has missed the developmental experience the building would have provided. Aggregated across millions of individuals and sustained across years, the displacement produces the generational patterns Twenge's longitudinal data reveals. The mechanism operated through smartphones against social and emotional development; it now operates through AI against cognitive development.