Charles Duhigg

how to believe—happens whenever people come together to help one another change. Belief is easier when it occurs within a community

twenty-four hours, his dehydration was so pronounced that a panicked Beverly took him to the emergency room. His temperature started rising, hitting 105 degrees as he sweated a yellow halo of perspiration onto the hospital’s sheets. He became delirious, then violent, yelling and pushing when nurses tried to insert an IV into his arm. Only after sedation

“All our life, so far as it has definite form, is but a mass of habits,” William James wrote in 1892.prl.2 Most of the choices we make each day may feel like the products of well-considered decision making, but they’re not. They’re habits. And though each habit means relatively little on its own, over time, the meals we order, what we say to our kids each night, whether we save or spend, how often we exercise, and the way we organize our thoughts and work routines have enormous impacts on our health, productivity, financial security, and happiness.

One paper published by a Duke University researcher in 2006 found that more than 40 percent of the actions people performed each day weren’t actual decisions, but habits.prl.3

He could remember most of the events in his life that had occurred prior to about 1960.

Habits can be changed, if we understand how they work.

As the route became more and more automatic, each rat started thinking less and less.

Habits, scientists say, emerge because the brain is constantly looking for ways to save effort. Left to its own devices, the brain will try to make almost any routine into a habit, because habits allow our minds to ramp down more often. This effort-saving instinct is a huge advantage. An efficient brain requires less room, which makes for a smaller head, which makes childbirth easier and therefore causes fewer infant and mother deaths. An efficient brain also allows us to stop thinking constantly about basic behaviors, such as walking and choosing what to eat, so we can devote mental energy to inventing spears, irrigation systems, and, eventually, airplanes and video games.

He created a craving. And that craving, it turns out, is what makes cues and rewards work. That craving is what powers the habit loop.

First, find a simple and obvious cue.

Second, clearly define the rewards.

If you get those elements right, Hopkins promised, it was like magic. Look at Pepsodent: He had identified a cue—tooth film—and a reward—beautiful teeth—that had persuaded millions to start a daily ritual. Even today, Hopkins’s rules are a staple of marketing textbooks and the foundation of millions of ad campaigns.

And those same principles have been used to create thousands of other habits—often without people realizing how closely they are hewing to Hopkins’s formula. Studies of people who have successfully started new exercise routines, for instance, show they are more likely to stick with a workout plan if they choose a specific cue, such as running as soon as they get home from work, and a clear reward, such as a beer or an evening of guilt-free television.2.13Research on dieting says creating new food habits requires a predetermined cue—such as planning menus in advance—and simple rewards for dieters when they stick to their intentions.2.14

“The time has come when advertising has in some hands reached the status of a science,” Hopkins wrote. “Advertising, once a gamble, has thus become, under able direction, one of the safest of business ventures.”

It’s quite a boast. However, it turns out that Hopkins’s two rules aren’t enough. There’s also a third rule that must be satisfied to create a habit—a rule so subtle that Hopkins himself relied on it without knowing it existed. It explains everything from why it’s so hard to ignore a box of doughnuts to how a morning jog can become a nearly effortless routine.