Scientists at Stanford were the first to discover a correlation between willpower and success. Further studies a few decades later uncovered that not only is it correlated with success, but that willpower is a muscle that can be fatigued. The implications of this in the workplace are significant. One 2010 study at a manufacturing plant in Ohio found that by addressing factors that taxed willpower, assembly line workers increased productivity at the plant by twenty percent within two months. How did they help these workers bring more of their willpower to the job? They gave them more control.

In 1998, a group of psychologists at Case Western Reserve University picked up on some of the research that started at Stanford a few decades earlier. The accepted wisdom at the time was that willpower was a skill that was learned. But for these researchers, this did not fit. A skill, like making an omelette, is something that can be done just as easily on Wednesday morning as Sunday afternoon. However, we all know that willpower can vary dramatically from day to day and hour to hour. The psychologists hypothesized that willpower was more like a muscle. A muscle that can get tired.

To test their hypothesis, 67 graduates were invited to participate in an experiment. Each participant was asked to skip a meal prior to arriving and then placed in front of two bowls. One had freshly baked chocolate chip cookies, the other radishes. Then the students were told a lie. They were told that they were part of an experiment testing taste perceptions. Then half the students were told they could eat the cookies, but not the radishes. The other half was allowed to eat the radishes, but not the cookies. After eating, they were all asked to wait fifteen minutes to allow the sensory memory of the taste to disappear. To pass the time they should work on a puzzle. It was implied that the puzzle wasn’t too challenging, but in reality it was impossible to solve. Then the experimenters left the room, sat back and watched through a two-way mirror. Resisting radishes isn’t too hard, but resisting freshly baked cookies when you’re hungry takes a lot of willpower. Some of these students who were told not to eat the cookies would pick the cookies up and look at them, or smell them. Some even licked the chocolate that had melted on their fingers. These students quickly became frustrated with the puzzle. Some would mutter in frustration or put their head down on the table and close their eyes. They persisted on average for eight minutes. The students that hadn’t used any willpower resisting yummy cookies faired much better. They looked relaxed and would attempt the puzzle again and again. Some went over half an hour before experimenters would come in and ask them to stop. On average, this group lasted 20 minutes.

Since this experiment was done, more than 200 other experiments have all found the same thing: willpower isn’t just a skill, it’s a muscle.

Research turned to whether willpower could be taught, developed, and what factors could help increase it. One of the original psychologists, Mark Muraven at the University of Albany, set up a new experiment.

He filled a room with students and put freshly baked cookies in front of them. They he asked the students to ignore the cookies, but they were treated kindly. The students were told the experiment was designed to measure their ability to resist temptations. They were thanked for contributing their time. They were asked, if afterwards, they had thoughts on how to improve this experiment, to let the researchers know. The other half were simply given orders: don’t eat the cookies, we’ll start now. Then both groups were ignore for five minutes. No one gave into temptation.

Afterwards, both groups moved onto part two of the experiment. They were asked to stare at a computer while numbers flashed for 500 milliseconds. Every time a six followed by a four flashed before them, they were supposed to push the spacebar. Focusing on this task for any period of time takes a fair bit of willpower.

The students who were treated kindly did well on the computer test. They pounced on the spacebar. They were able to maintain their focus for the entire 12 minutes. Despite ignoring the cookies, they had willpower to spare. Students who had been treated rudely however, did terribly. They kept forgetting to hit the spacebar. They said they were tired and couldn’t focus. Their willpower muscle had been fatigued more than the students who’d been treated kindly.

When Mark started exploring why students who had been treated kindly had more willpower, he found that the key difference was the sense of control they had over their experience. “We found this again and again,” Muravan told Charles Duhigg, author of The Power of Habit. “When people do something that they think is for personal reasons, or they have a choice, or it’s for someone they care about, the task is much less taxing. They feel like they have no autonomy if they’re just following orders. Willpower muscles get tired much faster.”

Extending this to the workplace, simply giving employees a sense of purpose, a feeling that they are in control, that they have genuine decision making authority, can radically increase how much motivation they bring to their jobs.

At a manufacturing plant in Ohio referenced in the opening paragraph, assembly line workers were empowered to make small decisions about their schedules and work environment. They designed their own uniforms and had authority over shifts. Nothing else changed. All the processes and pay scales stayed the same. Within two months productivity at the plant increased by 20 percent. Workers were taking shorter breaks and there were fewer mistakes. Giving employees a sense of control impacted how much self discipline they brought to their jobs.

Starbucks has focused on the lessons of chocolate chip cookies to a great extent. Starbucks understands that the amount of willpower baristas bring to dealing with clients in a friendly, happy way has a direct impact on bottom line results. During a phase or tremendous growth, the company lost their way for a period of time. Customer satisfaction suffered and so did financial results. While refocusing involved several strategies, one of the keys was refocusing on the barista.

To give employees a great sense of control and increase motivation to provide great service, they allow employees to make decisions about how they’ll provide great coffee and a great experience. Store staff decide how espresso machines and cash registers are laid out. They decide for themselves how customers should be greeted and where merchandise should be displayed. It’s not unusual for a store manager to discuss for a couple hours where a blender should be located. They started asking their employees to use their intellect and creativity and stopped telling them what to do. They understood that people want to be in control of their lives. Since then, turnover has gone down and customer satisfaction is up.