As 2015 draws to a close, perhaps you’re thinking about what you’d like to do differently next year. Whether it’s holding your tongue, spending more wisely or simply eating a more varied diet, the days are approaching when new year’s resolutions are set.

According to a YouGov survey last December, 2015 was the year in which 63% of us planned to turn over a new leaf. Losing weight, getting fitter and eating more healthily topped our wish list, while 12% of us strove to achieve a healthier work-life balance. How many achieved their goals is unclear, but, if experience is anything to go by, there are good grounds to be pessimistic. Of those surveyed, 32% pointed out that their resolutions are usually broken by the end of January, while only 10% said they never break one.

What is it that separates the resolute minority from the fallen masses? Is it just a matter of willpower or are other powers at work? And can psychological research teach us anything about how to make better resolutions in 2016?

New year’s resolutions have a long history. The Babylonians pledged to return borrowed objects and repay their debts at the start of each year, while the Romans kicked off January by making a vow to the god Janus (from whom the month takes its name). That’s centuries of potential for broken promises.

“I think the main reason why new year’s resolutions fail is people being unrealistic,” says Benjamin Gardner, an expert in behaviour change at King’s College London. “If you’re not doing any exercise and set yourself the goal of going to the gym five times a week for half an hour, you’re probably not going to achieve it. The other reason is people not necessarily being ready to change.”

Psychologists recently proposed that, for behaviour change to occur, people must have the capability, opportunity and motivation to make it happen. Often people aren’t making resolutions for the right reasons, says Gardner: “They think that because it’s new year, they’re obliged to say they’ll change their behaviour. But once they face the reality of what they’re doing, they give up because they aren’t motivated enough in the first place.”

How do you go about choosing smarter resolutions?

The first question to ask yourself is: if there were no pressure from anyone else, what would you, personally, like to change? This is important, because studies have indicated that people are more likely to succeed in changing their behaviour when they are motivated by internal rather than external forces. For instance, a 1996 study of 128 obese people who enrolled on a six-month weight-loss programme found that those who were internally motivated by factors such as wanting to make the change for the sake of their health were more likely to regularly attend the sessions, lost more weight and were more likely to keep it off over the long term than those who were motivated by pressure from, say, friends and family.

Assuming you are making a resolution for the right reasons, the next question is: are you physically and psychologically capable of doing what it takes to succeed?

Many people assume that willpower is a character trait that you’re either born in with, or innately lack. But recent psychological research suggests that willpower is more complex than that: it can be trained, but it also relies on energy and can become depleted if you overuse it. “Just like a muscle, the amount of willpower you have at any given time rises and falls, and if you exercise it, it gets stronger,” says Roy Baumeister at Florida State University in Tallahassee.

In a now classic experiment, he invited one group of volunteers to eat a batch of chocolate chip cookies and asked another group to resist the cookies (which remained available) and eat radishes instead. All the volunteers were then given a difficult geometry puzzle to solve and monitored to see how long they stuck at it. Those who ate the cookies spent far longer on the puzzle than those who ate the radishes, providing one of the first clues that willpower is a resource that can be used up. Subsequent experiments have shown people also find it harder to exert self-control after making decisions; and when their blood sugar is low.

“I often think of politicians who get into trouble with drugs or prostitutes, or whatever,” says Baumeister. “While I’m not making excuses for them, spending all day making decisions is likely to deplete their willpower and then, without realising it, they find themselves in a compromised state.”

However, he points out that more mundane activities can also dampen your resolve: “Little acts of self-control, such as resisting a desire, making yourself do something you don’t want to, not going to the bathroom when you need to… all of these are a drain on your willpower.”

Making several resolutions at once, then, could be self-defeating; if you’re using energy to work on one, you’ll probably have less willpower available for all of them. Instead, Baumeister advises doing them in sequence, starting with the easiest. This is because willpower appears to grow stronger the more it is exercised – provided you don’t overdo it, of course. For instance, several studies have shown that when volunteers are given small and regular self-control challenges for a week or two, their willpower significantly improves.

“Doing something that taxes your willpower every once in a while, such as taking a cold shower in the morning, going for a run even when it is raining, or doing a very hard workout, may help to ‘activate’ your willpower,” says Katharina Bernecker, a psychologist at the University of Zurich, though she adds more research is needed to explain how such willpower challenges work.

Is willpower enough?

Even if willpower isn’t standing in the way of achieving your goals, other things might be. You also need to question if you have the opportunity to change your behaviour, or whether there are obstacles in your path.

“In our research, we can show again and again that having a goal that specifies a desired outcome or behaviour is not good enough,” says Peter Gollwitzer, professor of psychology at New York University. It might be OK if your goal is simple, like buying a cup of coffee on your way to work each morning, but if it’s more complex, like resolving to tackle difficult emails as soon as you sit down at your desk, you may struggle. It’s known as the “intention behaviour gap”.

“Not only do your goals have to be desirable, achievable and have a specific outcome, you also need to think about the when, where and how,” Gollwitzer says. “You need to identify a good opportunity to get started and to plan for the different obstacles you might encounter and how to deal with them.”

Say 2016 is the year you plan to write a novel. First, you need to identify good situations in which to initiate your writing: it could be whenever your partner goes out to their gym class. But you also need to plan what to do if your best friend calls and suggests you meet for lunch instead. Gollwitzer calls this “if-then planning”: if X happens, then I will do Y.

He has found that people are two to three times more likely to achieve their goals if they use an “if-then” plan; this goes for all sorts of goals, from weight loss to using more public transport.

One reason why this form of planning seems to be so effective is that it often involves tying behaviours to specific cues in your environment. In other words, once you’ve made your plan, you no longer have to expend mental energy making choices and can more or less function on autopilot: you’ve created a habit.

Of course, habits are often the very reason people need to make new year’s resolutions in the first place. “The good thing about habits is that they’re very mentally efficient; they allow us to do things without thinking about doing them, which is great for things that we need to do frequently and are adaptive responses to cues in our environment,” says Gardner. “However, when we form undesirable habits, it creates a real challenge because your habits are not in line with your motivations.”

Take the common resolution to eat more healthily. One reason this is often so difficult to achieve could be that we begin to form bad eating habits over Christmas and this continues into the new year, despite our best intentions. Last year, American research revealed that – in line with healthy eating resolutions – supermarket sales of healthy foods increased 18.9% in January-March, compared with the Christmas holiday. However, sales of less healthy foods remained at holiday levels and households continued to consume more calories overall. This suggests that people adjust to a new “status quo” of overeating that continues into the new year, says Lizzy Pope at the University of Vermont, who led the study.

“Buying lots of healthy food is wonderful if you’re trying to eat healthier, but the other half of the equation is to decrease your purchase and consumption of less healthy items,” she says. “Before going to the grocery store, it may be helpful to make a list; to mentally divide your cart and fill at least half with healthy items; and to try not to go on autopilot when you’re attempting to initiate good habits after the new year.”

Can I change my habits?

Habits form through repetition of the same behaviour in response to the same cue. Gardner has discovered that the first few times you do something are the most strongly habit-forming; although separate research suggests it takes 66 days on average to form a new habit. This study also revealed that some behaviours are easier to habitualise than others. For instance, simple actions, such as drinking an extra glass of water after breakfast, seem to become habitual more quickly and more strongly than more complex ones, like doing 50 sit-ups. “That tells us that you should try and pick small behaviours to change and build them up until you reach your overarching goal,” Gardner suggests.

In terms of breaking bad habits, it’s often a good idea to find something to replace them with. “If all you’re doing is saying: ‘I won’t drink a glass of wine while I’m cooking,’ and you’ve got a bottle of wine in front of you, you’ll keep having to fight the impulse until at last your willpower is exhausted,” Gardner says. “You need to distract yourself, or do something else.”

new year’s resolutions Photograph: muharrem Aner/Getty Images

Of course, another way to deal with such obstacles is to remove them from the outset, so you won’t have to deploy your willpower to fight them. Molly Crockett at the University of Oxford dubs this strategy “precommitment”, although it could also be described as removing temptations in advance, so that your future self won’t have access to them. When she and her colleagues offered volunteers a choice between an immediate small reward or a larger reward if they waited, they found that people often buckled and took the small reward if they were intermittently reminded about it, but if they pre-committed to taking the larger reward, they were more likely to reap it.

This study also revealed that an area of the brain involved in thinking about the future becomes activated during pre-commitment and this interacts with another brain area involved in self-control. “All things being equal, we have found that pre-commitment is a more effective self-control strategy than willpower,” says Crockett. “If you’re trying to lose weight, for example, it’s better to avoid buying unhealthy foods in the first place than to have them around and expect you’ll be able to resist them.”

So when it comes to new year’s resolutions, breaking your goals into simple, specific behaviours that you can habitualise seems to be a good strategy, at least if you listen to the experts. But do these behaviour-change gurus practise what they preach, or are they are bad as the rest of us in making – and breaking – their resolutions?

Asked if, as a result of his research, he’s now a super-achiever, Gollwitzer breaks the auditory equivalent of a smug grin. “I would say so, yes.” Although he continues: “When I decide to make a new year’s resolution, I smile because I know that now I have to make a plan. Then I immediately move on and ask OK: what is the obstacle? And then I realise OK, well maybe I don’t really need to be worried about this, after all.”

Sometimes there’s a very good reason why we’re not slimmer/fitter/richer/nicer than we already are. And that’s because, if we’re completely honest with ourselves, we don’t really need to be.