More than 40% of the things we do in a day aren’t really decisions — they’re habits.

But changing habits isn't a matter of "powering through" them. Like a muscle, your willpower gets exhausted throughout a day.

As Charles Duhigg details in the now-in-paperback "The Power of Habit," advances in social science suggest that behavioral change isn’t a result of focusing on the behavior itself. Instead, we need to tinker with the cues and rewards that keep the habit coming.

To change a habit, you have to first understand how it forms.

A habit is not one action but a loop, made up of a cue, routine, and reward:

The cue is what triggers a behavior to start. It tells your brain to switch into automatic mode. There are five primary types of cues: a place, a time of day, a particular person, a particular emotion, or a ritualized behavior. As Duhigg told the Boston Globe , he had a cookie habit, one that led to his gaining eight pounds. Every day between 3 and 3:30 p.m., he’d get up from his desk, go crab a cookie from the cafeteria, and eat the sweet snack while talking with his coworkers.

the Boston Globe Then there’s the routine, the automatic behavior that you find yourself doing unknowingly. While having a habit being automatic sounds unnerving, it's actually an adaptation . The first time you do something in your life — like driving a car — you have to invest a ton of attention into it. But the more you do something, the less attention you need to invest in it — good drivers can hold a conversation while parallel parking. That's because you’ve become so familiar with an activity that you no longer are making decisions about it. The habitual behavior just takes over, freeing up mental space.

. The first time you do something in your life — like driving a car — you have to invest a ton of attention into it. But the more you do something, the less attention you need to invest in it — good drivers can hold a conversation while parallel parking. That's because you’ve become so familiar with an activity that you no longer are making decisions about it. The habitual behavior just takes over, freeing up mental space. Lastly, there’s the reward, the pleasure you get from the behavior. Beyond feeling good, the reward burns the habit into your memory, making it a go-to action for the next time a cue occurs.

Understanding the cue and reward can curb a bad habit.

In the case of Duhigg and his cookies, the author didn’t know what reward was driving his snacking. To find out, he did an experiment over a few days.

On the first day he went for walk around the block when the cookie urge struck, since that would test whether he just wanted a break from work. The next day he grabbed a candy bar and ate it back at his desk, since that would satisfy any possible sweet tooth. Then on another day he went to the cafeteria but didn’t buy anything — instead he just walked up to a colleague and started chatting.

“What I figured out pretty quickly, was (that the reward) had nothing to do with cookies,” he said. “It had to do with socializing.”

So now, instead of gobbling a cookie and gabbing with a friend at 3:30, he gets up from his desk, ambles over to a colleague, and gossips for 10 minutes. Then he goes back to work. The urge to get the cookie has disappeared, he reports, no sweets needed. And he’s lost 12 pounds.

You can use rewards to create habits, too.

Let’s say you don’t want to stop eating cookies. Instead, you want to go for a run every day. Knowing how cues and rewards form behaviors can help.

It’s a matter of teaching your brain to associate exercise with a reward, Duhigg says. Regular runners might crave the endorphin rush that comes after a run, but as a beginner, you might need some help. To do that, he says, give yourself something you love after the workout, like say, a cookie:

This is counterintuitive, because most people start exercising to lose weight. But the goal here is to train your brain to associate a certain cue ("It's 5 o'clock") with a routine ("Three miles down!") and a reward ("Chocolate!"). Eventually, your brain will start expecting the reward inherent in exercise ("It's 5 o'clock. Three miles down! Endorphin rush!") and you won't need the chocolate anymore. In fact, you won't even want it. But until your neurology learns to enjoy those endorphins and the other rewards inherent in exercise, you need to jump-start the process.

So either way the cookie crumbles, knowing your cues and rewards can help you change your habits.