A day before President Obama addresses the Democratic National Convention Thursday night, Vanity Fair has released excerpts of an interview the president gave to the magazine that might in part explain his trademark cool demeanor.

Obama told Vanity Fair he's best when he believes what he's saying, and that it's insulting for him to fake emotion.

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"For me to feign outrage, for example, feels to me like I'm not taking the American people seriously. I'm absolutely positive that I'm serving the American people better if I'm maintaining my authenticity. And that's an overused word. And these days people practice being authentic. But I'm at my best when I believe what I am saying," the president told financial writer and best-selling author Michael Lewis in a wide-ranging interview for the October issue of Vanity Fair.

Obama said it's important for him to stay connected to Americans to avoid getting overwhelmed by the decisions he faces.

"One of my most important tasks is making sure I stay open to people, and the meaning of what I'm doing, but not to get so overwhelmed by it that it's paralyzing. Option one is to go through the motions. That I think is a disaster for a president. But there is the other danger," he told Lewis, according to the interview excerpts. "There are times when I have to save it and let it out at the end of the day."

Being president is a game of probabilities, Obama told Lewis.

"Nothing comes to my desk that is perfectly solvable," Obama told Lewis. "Otherwise, someone else would have solved it. So you wind up dealing with probabilities. Any given decision you make you'll wind up with a 30 to 40 percent chance that it isn't going to work. You have to own that and feel comfortable with the way you made the decision. You can't be paralyzed by the fact that it might not work out."

One way to tackle the weight of the office, Obama said, was to stay physically active.

"You have to exercise," he said, "or at some point you'll just break down."

Obama, who wears high-tops stamped with "44? when he plays basketball, also told Lewis it's important to stick to a routine.

"I'm trying to pare down decisions. I don't want to make decisions about what I'm eating or wearing. Because I have too many other decisions to make," Obama told Lewis. "You need to focus your decision-making energy. You need to routinize yourself. You can't be going through the day distracted by trivia."