True wisdom is less presuming than folly. The wise man doubteth often, and changeth his mind; the fool is obstinate, and doubteth not; he knoweth all things but his own ignorance.

The saying contrasts intellectual humility with the overconfidence of ignorance. “True wisdom” is portrayed as cautious and self-correcting: the wise person revises beliefs in light of new evidence and is comfortable with uncertainty. Folly, by contrast, is marked by obstinacy and a false sense of omniscience—especially an inability to recognize one’s own limitations (“his own ignorance”). The aphorism anticipates later philosophical themes (Socratic awareness of not-knowing; fallibilism) and functions as a moral warning against dogmatism: certainty can be a symptom of shallow understanding, while doubt can be a sign of genuine insight.