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IT HAS been a long day. You’ve been squinting at spreadsheets since 9 am, but your boss keeps interrupting to ask how you’re getting on and colleagues insist on offloading their own problems. By 6 pm you’re exhausted. It’s a miracle that you even make it home before hitting the wine and chocolate.

Psychologists used to have a convincing explanation for why days like these leave us weak in the face of temptation. Willpower is a limited resource that, like the cash you work so hard for, will eventually run out. Use it all up during the day and there’ll be none left by dinner time.

This much has been received wisdom in psychology circles for nearly 20 years. Recently, though, that certainty has begun to fade. According to a series of newer findings, our levels of self-control are not so much a budget we have to eke out, but a renewable resource that can be powered up as we go along. “Instead of thinking of willpower as the amount of petrol in a car… think of it as the car’s battery,” says Krishna Savani at Nanyang Technological University in Singapore. “The more you drive, the more the battery gets charged, and the longer it will last.”

In this view, your powers of concentration are only limited if you think they are. It raises the intriguing possibility that, if we can get into the right mindset, superhuman powers of motivation and self-control could be ours for the taking.

This new way of thinking about motivation comes on the heels of a growing realisation in psychology that what you believe about your own ability matters. More than 40 years ago, the Stanford psychologist Carol Dweck became fascinated by differences in the way that children dealt with setbacks in their schoolwork. While some of them were quick to quit, others simply redoubled their efforts. The quitters, Dweck found, blamed their difficulties on lack of ability and felt that they would never make the grade. The more determined children, by contrast, were more motivated by learning itself than by getting good grades, and they tended to see ability as fuelled by effort, rather than set in stone.

Resistance is fruitful

Dweck refers to these as fixed and growth mindsets respectively, and believes that our mindset dictates how we tackle problems throughout our lives. It’s an idea that has resonated: Dweck’s 2006 book became a bestseller and her has been viewed more than 6 million times.

Even with a growth mindset, though, no one succeeds without self-discipline. This harsh fact of life led Dweck and others to take a fresh look at what willpower is and why some of us have more of it than others.

It is certainly important. We have known for some time that the ability to delay gratification in pursuit of longer-term goals has a big impact on our lives. Back in the late 1960s, first tested the powers of 4 to 6-year-old children to resist sweets, in what has become a classic psychology experiment. He placed a marshmallow in front of each child and left the room for 15 minutes, telling them that if the sweet was still there when he returned, they would be rewarded with two. Those who managed to resist temptation long enough to get double helpings went on to be more successful later in life, education and their careers.

More recently, for decades discovered that those with the least self-control as young children grew up to exert a significantly greater burden on society as adults, with higher rates of unemployment, poor health and criminality.

According to the idea that willpower is limited – known as ego-depletion theory – the difference in people’s ability to stay strong in the face of temptation can be explained by the amount of fuel in our mental reserves. Social psychologist Roy Baumeister, then at Case Western Reserve University in Cleveland, Ohio, came up with the idea in 1998 after a series of experiments. When people were asked to concentrate on solving a difficult maze, say, or a series of anagrams, their performance on a second mentally taxing task dropped compared with control volunteers whose initial task was easy. He concluded that willpower is like a muscle that gets fatigued with overuse.

“Self-control is like a car battery: the more you drive, the longer it will last”

Something similar happened when rather than mental exercise, the exertion takes the form of resisting temptation. In , people told to ignore freshly baked cookies in favour of radishes subsequently showed less persistence at a tricky task that involved drawing geometric shapes. Since Baumeister’s initial studies, more than 100 others have shown this same pattern – tax somebody’s mental energy in any way and their powers of concentration and ability to resist temptation will take a hit.

Baumeister and his colleagues went on to suggest that the currency of this effect is glucose, which gets used up faster when our brains have had to work hard. In their experiments, . In 2012, the American Psychological Association published a on the psychology of willpower that recommended eating regular snacks as a way to “prevent the effects of willpower depletion”.

Soon afterwards, though, the cracks began to appear. In 2015, the authors of a of published and unpublished data claimed that in fact there is virtually no evidence for ego depletion, a claim that was swiftly countered by . A involving 26 labs around the world also found almost no evidence for an ego-depletion effect.

To add to the confusion, the labs, which all followed the same protocol, had used just one way of inducing ego depletion, which they admit may not have been lengthy or arduous enough to induce such depletion in many participants. Overall, the report’s authors concluded that estimates for the size of the ego-depletion effect should be revised down. They later wrote, .

Seeing willpower and motivation as being more about mindset than blood sugar level might help clear the confusion. In 2010, Dweck and her colleagues Veronika Job at the University of Zurich and Gregory Walton, also at Stanford, repeated Baumeister’s experiments, but beforehand whether they considered willpower to be a limited resource depleted by effort. They found that those who believed that willpower is finite showed the usual ego-depletion effect, whereas those who believed that willpower is potentially unlimited showed no signs of running out of steam in the second task.

Further studies have discovered that you can improve willpower just by telling people that such a thing is possible. When people were shown statements such as “it is energising to be fully absorbed with a demanding mental task”, they continued to improve through a tough 20-minute memory challenge. Another group that was told willpower is limited .

can also prevent ego depletion by upping the incentive. Again, the message seems to be that where there’s a will, there’s a way. Our performance may tend to decline if we’re repeatedly challenged, but with enough motivation, our reserves of willpower suddenly seem a lot more bountiful.

Meanwhile, other research has directly challenged the idea that glucose is the source from which willpower springs. Several studies, and , have shown that when volunteers gargled a sugary drink before or during a mental challenge, it prevented ego depletion, even if they spat the drink out. This suggests that merely the suggestion of a fuel top-up is enough to keep mental exhaustion at bay.

“Those who believed that willpower is potentially unlimited showed no signs of running out of steam”

This is tricky for the ego-depletion theory to explain because gargling doesn’t allow time for glucose to be metabolised. It is also more than a placebo, because gargling an artificially sweetened drink doesn’t have the same effect. Most explanations for why it works have to do with motivation, which chimes with the research on the importance of mindset. One possibility is that glucose in the mouth triggers reward-related brain activity that makes the challenge seem more rewarding and hence makes it easier to keep going. This supports the idea that belief and desire are crucial for our powers of perseverance, rather than some magical well of willpower.

Baumeister, though, isn’t too fazed by this line of research. “The work is quite creative but does not require a major revision of our understanding,” he says. “Usually what is in the mouth is soon in the belly, so tasting glucose signals that it is fine to allocate more resources now, as they will be replenished.”

Baumeister recently revised his theory to take this into account. In a published last year with his colleague Kathleen Vohs at the University of Minnesota, he argues that while there is a limited resource behind self-control, it rarely, if ever, runs dry. According to the revised theory, whether we are able to maintain self-control comes down to our judgement about how much willpower juice we have left and how we choose to allocate these reserves. As with physical effort, in which our muscles feel tired long before they are close to collapse, how long we can keep going is all about how much energy we think is left.

This revised version of ego-depletion theory can better account for the findings showing that mindset is important. After all, if you think willpower is unlimited, you’re more likely to be willing to allocate the extra energy needed to keep going at repeated tasks. But that doesn’t mean willpower is literally unlimited, say Baumeister and Vohs, who argue that if it really were possible to eliminate failures of self-control “simply by cultivating belief in unlimited willpower, then presumably most successful cultures and individuals would have come round to that belief long ago”.

No more excuses

A , though, raises the possibility that some cultures may have done just that. Krishna Savani teamed up with Veronika Job to study volunteers in this country because of the widely held belief there that mental effort isn’t draining but energising. As an example, Savani and Job point to the common practice in India of teaching children and teens to focus on a candle in a dark room for 10 to 20 minutes without blinking or looking around. Reflecting this cultural attitude, the researchers cite figures suggesting that Indian kids tend to and than in , and . This is perhaps, at least in part, because the expenditure of mental effort is seen as purely beneficial, with no concerns about burnout.

Savani and Job wanted to see if the cultural belief that effort is energising would influence the way ego depletion works in India. If prompting people to think of exerting self-control as energising eliminates the ego-depletion effect, as Job’s earlier research showed, then perhaps people in India might be immune to ego depletion. In fact, when they repeated Baumeister’s experiments with hundreds of Indian participants, they actually showed a “reverse ego depletion” effect. When the first task was harder, they tended to perform better on the second task. Savani concluded that ego depletion is by no means an inevitable feature of human psychology.

“We no longer have an excuse for being lazy, saying: ‘Oh, I have worked so hard, I need a break’”

“We no longer have an excuse for being lazy, saying ‘Oh, I have worked so hard, I need a break’,” he says. “No matter how mentally tired you are, you always have mental capacity to concentrate on and work on a given task.” For his part, Baumeister told us that this new “profoundly important” research from India is “truly fascinating” and he acknowledged that “if born out by further work [it] could really bring about major revisions to our understanding”.

If replicated – and we still don’t know whether this effect also applies to tests of self-control based on temptation as well as mental concentration – it could mean that seemingly superhuman powers of willpower and self-control may be within our reach, given the right mindset and a little practice. Taken with the other findings, it seems that there is a powerful psychological component to how much willpower we can muster in any given situation. See mental challenges and resistance to temptation as energising rather than draining, and your beliefs may well become self-fulfilling.

It may well be worth the effort. According to a recent survey of , those who believed that willpower is unlimited were not only happier, but suffered less from stress and bad moods when exam time approached. Diaries that the students kept suggested this was because they were able to step up their efforts to meet increasing challenges. Another survey of contributors to a stress and burnout online forum found that those who endorsed the “willpower is unlimited” idea were .

In short, no matter how much you have to do, you probably have more willpower reserves than you think. Your chances of future success and happiness may depend on learning to tap into them. No pressure, then.

This article appeared in print under the headline “Yes you can!”