From Lewis's article ...
This time he covered a lot more ground and was willing to talk about the mundane details of presidential existence. “You have to exercise,” he said, for instance. “Or at some point you’ll just break down.” You also need to remove from your life the day-to-day problems that absorb most people for meaningful parts of their day. “You’ll see I wear only gray or blue suits,” he said. “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.” He mentioned research that shows the simple act of making decisions degrades one’s ability to make further decisions. It’s why shopping is so exhausting. “You need to focus your decision-making energy. You need to routinize yourself. You can’t be going through the day distracted by trivia.” The self-discipline he believes is required to do the job well comes at a high price. “You can’t wander around,” he said. “It’s much harder to be surprised. You don’t have those moments of serendipity. You don’t bump into a friend in a restaurant you haven’t seen in years. The loss of anonymity and the loss of surprise is an unnatural state. You adapt to it, but you don’t get used to it—at least I don’t.”
But if you happen to be president just now, what you are faced with, mainly, is not a public-relations problem but an endless string of decisions. Putting it the way George W. Bush did sounded silly but he was right: the president is a decider. Many if not most of his decisions are thrust upon the president, out of the blue, by events beyond his control: oil spills, financial panics, pandemics, earthquakes, fires, coups, invasions, underwear bombers, movie-theater shooters, and on and on and on. They don’t order themselves neatly for his consideration but come in waves, jumbled on top of each other. “Nothing comes to my desk that is perfectly solvable,” Obama said at one point. “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.” On top of all of this, after you have made your decision, you need to feign total certainty about it. People being led do not want to think probabilistically.