SANTA CRUZ, Calif. -- We've all tried to ignore that seductive whisper in our head at some point in our lives -- the one urging us to snag a bigger piece of chocolate cake or take a breather from that mind-numbing spreadsheet.
Some of us are better at denying temptation, while others give in. We tell ourselves that after a hard day of work, we need to rest and recharge.
But our ability to power through difficult tasks or deny ourselves that extra piece of pepperoni pizza is all in how we think about willpower, according to a recent Stanford University study.
Giving hope to the gluttons and procrastinators of the world, the study suggests that people have more of an ability to regulate their behaviors than they think.
The Stanford researchers said people generally fall into two groups. One believes that a person's willpower doesn't run out -- that it's "unlimited." The second group believes that a person can run out of willpower after a hard task like taking a final exam -- because willpower is "limited."
"Self-control is something that everybody is confronted with, at least at some periods of their lives," said Veronika Job, lead author of the study. She said it's especially important for groups like diabetics, who have to practice self-control constantly.
"We know that behavioral change is a cycle," said Heather Schwartz, a medical nutrition therapist at Stanford Hospital & Clinics. For her diabetic patients, sticking to their health plan is a constant battle.
"They get on the bus, they get off the bus."
For Ms. Job, the notion that someone could just run out of willpower after a short period of time was just too simplistic. "It can't be that simple -- that after 10 minutes you're just depleted and you can't proceed with the same energy and strength anymore," she said.
So she and her co-authors ran experiments to see how perceptions of willpower influenced how well their test subjects -- Stanford undergraduates -- performed on a series of tasks. The researchers conducted lab experiments and a "real world" experiment during finals week.
In the lab experiments, students were asked to fill out a questionnaire designed to determine whether they thought of willpower as limited or unlimited. The researchers then split them into two random groups.
The groups were then asked to complete two tasks. But one group of students had it easy, while the second group was put through the wringer.
For the first group, students spent five minutes crossing out every letter "e'' from a page of text.
Students in the second group spent five minutes following a complex set of rules that only sometimes required them to cross out the letter "e" from a page of text.
Then both groups were asked to identify the color a word was written in on a computer screen. But the words themselves were colors. For example, the word "red" might be written in a blue font, and the students would have to identify the color blue to get a correct score.
For the students who believed that willpower was unlimited, Ms. Job found that they were just as accurate on the color test regardless of whether they were in the easy group or the hard group. But for students who viewed willpower as limited, they did worse on the color test after finishing the difficult task.
But researchers didn't stop there. They wanted to see if people could be trained to think of willpower in one way or the other.
Ms. Job, who was a visiting researcher at Stanford and is now at the University of Zurich, found that she could reproduce these results with a group of students who were manipulated into thinking willpower was either unlimited or limited. They did this by having students fill out biased questionnaires, designed to get them thinking one way or the other.
Ms. Job and her colleagues then wanted to see whether what they were finding in the lab would translate to the real world. So they looked at how students' perception of willpower tracked with how well they could control behaviors such as procrastination and sticking to a set of goals during finals week.
Ms. Job found that the more students saw willpower as limited, the more they put things off and let their goals slip.
This isn't news to some college students. "I definitely understand hitting a wall," said Roy Lopez, a junior majoring in literature at the University of California-Santa Cruz who believes that willpower is limited. "You need some other influence to keep going."
"There's a panic during midterms and finals that keeps me focused," Mr. Lopez said.
While he believes you can train yourself to have more willpower, "it's harder to stay focused when there's no pressure."
The results of the study came as a welcome surprise to Ms. Schwartz, the medical nutrition therapist.
Ms. Schwartz said the study has given her a new way of thinking about willpower -- and helping her diabetic patients. She said that although the study's results made sense, framing willpower as something that could be manipulated was surprising to her. She had not thought about it that way before.
The finding that willpower is not a limited resource is "a pretty powerful conclusion," she said.
If a patient finds sticking to their goals difficult, Ms. Schwartz said, she can now tell them that the willpower is there -- and that they just have to "access it."
Ms. Schwartz said if the Stanford team does any work on willpower and diet, she would be extremely interested in the results.
"So many factors go into choosing foods," she said. Comfort, color preferences, smell -- all, she said, are things that could complicate how willpower determines whether someone falls off the wagon or not.