In reading the lives of great men, I found that the first victory they won was over themselves... self-discipline with all of them came first.

Truman frames “greatness” as beginning with an inward conquest rather than an outward one. By saying that the first victory of great men is “over themselves,” he emphasizes mastery of impulse, habit, and ego—qualities that enable sustained achievement in public life. The ellipsis underscores a practical conclusion: self-discipline is not an optional virtue but the foundation that precedes talent, opportunity, or acclaim. The remark also reflects a democratic, character-centered view of leadership: what distinguishes exemplary figures is not merely circumstance or brilliance, but the capacity to govern oneself—an ethic especially resonant with Truman’s reputation for plainspoken moral seriousness and responsibility.