Whatever you think of his politics, you have to admit that Barack Obama has a very demanding schedule. The president’s typical day might include a ceremony celebrating Team USA’s Olympic athletes, meetings with his cabinet and military advisors, several speeches to campaign supporters, and phone calls with foreign leaders.

In an article for October’s Vanity Fair, author Michael Lewis explored some of these behind-the-scenes details of President Obama’s daily life. To prepare for the article, Lewis spent six months in close company of the president — playing in his high-energy basketball games, sitting up front in Air Force One, and chatting with him whenever the president had a free moment.

There was one particular question that Lewis asked repeatedly of President Obama. Lewis presented the president with the following scenario: “Assume that in thirty minutes you will stop being president. I will take your place. Prepare me. Teach me how to be president.”

The president first touted the necessity of daily exercise — a habit that I endorse wholeheartedly. But what he said next was even more interesting: “You’ll see I wear only gray or blue suits. 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.”

I share President Obama’s practice of “routinizing the routine.” I eat essentially the same thing for breakfast each morning: a bowl of cold cereal and a banana. For lunch, I eat a chicken salad sandwich with a diet soda. Each morning, I dress in one of a small number of suits, each of which goes with particular shirts and ties.

Why do President Obama and I subject ourselves to such boring routines? Because both of us (especially President Obama!) make many decisions each day — decisions that are far more important to us than what we wear or what we eat for breakfast.

Making too many decisions about mundane details is a waste of a limited resource: your mental energy. In the late 1990s, Roy Baumeister (a professor at Florida State University) and colleagues performed several experiments showing that certain types of conscious mental actions appeared to draw from the same “energy source” — gradually diminishing our ability to make smart decisions throughout the day.

In one of Baumeister’s experiments, subjects were forced to eat a pair of radishes instead of the freshly baked, aromatic chocolate chip cookies sitting on the same table. In another, subjects were instructed to suppress their emotional reactions to a comedic or tragic film. In both cases, those subjects were quicker (relative to control groups) to give up on a problem-solving task that followed, suggesting that their previous acts of self-control and self-regulation — eating the radishes or maintaining a stoic appearance — had depleted their mental resources.

Over the past fifteen years, many researchers have replicated these experiments with slight variations, trying to discover which types of mental actions most quickly deplete our mental resources, and what some consequences of this depleted state might be. Chapter four in Dan Ariely’s new book The (Honest) Truth About Dishonesty summarizes some fascinating experiments that show that a tired brain makes us more likely to eat junk food, lie, or otherwise exhibit poor self-control.

Of particular interest to me (and, apparently, President Obama) are a series of experiments run by Kathleen Vohs (an associate business professor at the University of Minnesota) and colleagues, including Professor Baumeister.

Vohs’s experiments tested whether everyday choices — which candy bar to eat or what clothes to buy, for instance — wear down our mental energy. The results? Vohs and colleagues consistently found that making repeated choices depleted the mental energy of their subjects, even if those choices were mundane and relatively pleasant.

So, if you want to be able to have more mental resources throughout the day, you should identify the aspects of your life that you consider mundane — and then “routinize” those aspects as much as possible. In short, make fewer decisions.

To me, this means wearing dull clothing and eating the same breakfast and lunch nearly every weekday. My specific approach might not work for you — and that’s fine! Maybe your job requires you to dress for success (say, if you work in the media) or vary your daily nutrition (say, if you’re a pro athlete).

The point is that you should decide what you don’t care about and that you should learn how to run those parts of your life “on autopilot.” Instead of wasting your mental energy on things that you consider unimportant, save it for those decisions, activities, and people that matter most to you.