In this sharp, provocative study of human folly, Leo Markun argues that stupidity is not a fixed label but a relative failure of judgment shaped by circumstance, training, and temperament. He challenges the authority of intelligence tests, grades, brain measurements, and pseudosciences like phrenology, showing how chance, illness, injury, education, and opportunity all complicate any simple verdict on a person's mind. Through autobiographical reflection and literary and historical examples, he demonstrates how genius, courage, nonconformity, and even religious or political conviction are often mistaken for foolishness. At its core, the book is a spirited defense of independent thought. Markun exposes the dangers of blind faith, sectarian dogma, civic complacency, and narrow specialization, warning against "educated fools" who memorize facts without learning to think. Drawing on practical psychology and John Dewey's ideas, he presents thinking as problem solving rooted in experience, self-education, observation, humor, and self-control. The result is a witty, forceful call for intellectual honesty and disciplined, original judgment. This edition has been fully restored with modern typesetting, custom cover design.