Sometimes a man wants to be stupid if it lets him do a thing his cleverness forbids.

The line points to a common form of self-deception: people sometimes prefer not to know, or to act as if they don’t know, because clear understanding would impose moral or practical restraints. “Cleverness” here stands for insight, foresight, or conscience—an intelligence that anticipates consequences and therefore forbids certain actions. Choosing “stupidity” becomes a strategy for evading responsibility: if one can blunt awareness, one can proceed without the discomfort of guilt, doubt, or rational objection. Steinbeck’s phrasing suggests this is not an absence of intelligence but a willed narrowing of it, highlighting how desire can override judgment and how ignorance can be cultivated to make wrongdoing (or risky choices) feel permissible.