No man likes to have his intelligence or good faith questioned, especially if he has doubts about it himself.

Adams points to a common psychological reflex: people react most defensively when criticism touches an insecurity they already harbor. To have one’s intelligence or sincerity challenged is painful in any case, but it becomes intolerable when it echoes private doubts—because the external accusation threatens to confirm an internal fear. The remark also implies a social insight about argument and persuasion: questioning a person’s competence or good faith rarely produces openness; it more often provokes resentment and self-protective hostility. In Adams’s skeptical, often ironic cast of mind, the line reads as a dry observation about human vanity and the fragility of self-confidence.