A leading sociologist's groundbreaking three-decade study challenges outdated views of crime and character, revealing that traditional risk factors alone poorly predict children's futures. Between 1970 and 2020, the United States experienced a dramatic rise in crime and incarceration, followed by an unexpected decline. Along with plummeting violence came reductions in substance use, car accidents, child poverty, and lead exposure. By 2020, incarceration rates hit a twenty-five-year low, with African Americans benefiting the most. Yet these positive shifts have not registered in public discourse or policies, which continue to rely on outdated studies and reductive narratives of moral character and personal responsibility. A major reason for this oversight is how social scientists study youth development--typically through single-birth-cohort approaches that fail to capture generational change. In a pioneering three-decade study of over one thousand Chicago children across multiple cohorts, Robert J. Sampson challenges this convention. He finds that children with similar self-control and family backgrounds, born just a decade apart, experienced dramatically different life paths. Strikingly, children born in the mid-1980s faced twice the likelihood of arrest by their mid-twenties than those born ten years later. This research reframes deeply ingrained assumptions about ongoing social decline and the importance of individual fortitude. Sampson spotlights the role of shifting social conditions and structural change in driving measurable improvements in youth trajectories, along with new risks that threaten these gains. The era into which a child is born shapes their future as profoundly as race, upbringing, or neighborhood. To rethink progress, inequality, and policy, we must first acknowledge how time itself leaves a transformative mark on individual lives.