No man, however strong, can serve ten years as schoolmaster, priest, or senator, and remain fit for anything else.

Adams’s aphorism suggests that certain roles—teaching, clergy, and high political office—exert a long, narrowing pressure on character and intellect. Even a “strong” person, he implies, is shaped by the habits these professions demand: authority, routine, moral or ideological certainty, and constant performance before an audience. Over a decade, such conditioning can make one less adaptable, less curious, and less capable of independent judgment in other spheres. The line also carries Adams’s characteristic skepticism about institutions: they do not merely employ individuals; they refashion them, often at the cost of versatility and freshness of mind.