From the earliest days of his presidential campaign, those around Senator Barack Obama have heard the same mantra. He repeated it after he announced his candidacy and after debates, after victories and defeats.

“I need to get better,” he would say.

In the way Mr. Obama has trained himself for competition, he can sometimes seem as much athlete as politician. Even before he entered public life, he began honing not only his political skills, but also his mental and emotional ones. He developed a self-discipline so complete, friends and aides say, that he has established dominion over not only what he does but also how he feels. He does not easily exult, despair or anger: to do so would be an indulgence, a distraction from his goals. Instead, they say, he separates himself from the moment and assesses.

“He doesn’t inhale,” said David Axelrod, his chief strategist.