14 Surprising Things That Affect Your Willpower And Decision Making

President Obama only wears blue or gray suits.

As he tells Vanity Fair, it's a way of managing his willpower.

"I'm trying to pare down decisions," he says. "I don't want to make decisions about what I'm eating or wearing. Because I have too many other decisions to make."

Obama's focus on routine is backed up by research. Social psychologist Roy Baumeister has found that willpower is like a muscle - it can be strengthened or fatigued with use.

It's a crucial insight, given that a 2011 study of 1 million people around the world found that people think that self-control is their biggest weakness or character failure.

As Baumeister details in his book "Willpower: The Greatest Human Strength" and a New York Times Magazine cover story, willpower and decision-making are interconnected. The house you grew up in, the number of decisions you made today, and what your friends are doing all affect your decisions in weird ways. Here's a look at how.