Man has gone long enough, or even too long, without being man enough to face the simple truth that the trouble with man is man.

Thurber’s aphorism turns the search for external causes—fate, society, technology, enemies—back onto human nature itself. The wordplay (“man enough”) suggests that maturity and courage consist in accepting responsibility rather than inventing scapegoats. By calling the truth “simple,” the line implies that the real difficulty is not complexity but denial: people resist admitting that cruelty, folly, and self-deception originate within ordinary human motives. The statement also carries a moral warning: progress in institutions or inventions will not solve “the trouble” unless individuals confront their own tendencies toward irrationality and aggression.