We can be absolutely certain only about things we do not understand. A doctrine that is understood is shorn of its strength.

Hoffer is pointing to a paradox of belief: the strongest certainties often attach to what we cannot fully explain. When a doctrine is opaque, it can function as a badge of identity and a refuge from doubt; its vagueness lets adherents project hopes, fears, and moral absolutes onto it. Once a doctrine is genuinely understood—its assumptions, limits, tradeoffs, and internal tensions made visible—it loses some of its mobilizing power, because understanding invites nuance and admits complexity. The remark fits Hoffer’s broader skepticism about mass movements and ideological fervor: certainty can be less a mark of truth than a symptom of psychological need, and clarity can weaken fanaticism by restoring proportion.