When a generation talks just to itself, it becomes more filled with folly than it might have otherwise.

Brand’s remark warns about intellectual and cultural inbreeding: when a cohort primarily exchanges ideas within its own age group, it loses corrective feedback from people with different memories, incentives, and time horizons. The “folly” is not mere ignorance but the overconfidence and fashion-driven thinking that can arise when shared assumptions go unchallenged. Implicitly, the quote argues for intergenerational conversation—institutions, mentorship, and long-term perspectives—as a check on short-term enthusiasms and moral panics. It fits Brand’s broader interest in long-term thinking and systems that preserve knowledge across time, suggesting that wisdom is partly a function of cross-temporal dialogue rather than isolated peer consensus.