If your commitment to your New Year's resolutions has been flagging, a new study on willpower may help. The researchers claim that psychologists are looking at self-control the wrong way. It's not that you don't have it when you are tired, but you choose not to use it when you're tired or stressed.

It may seem like a minor difference, but it suggests the best way for people to exercise self-control is to change how you view tasks requiring self control. Instead of seeing them as unpleasant challenges ("No carbs after 4 o'clock!") and things you should do, if you can convince yourself that they're things that you want to do, it will make them much, much easier to accomplish.

The key is finding a way to want and like the goal that you are chasing. Some people do this naturally — think of the person who loves to run and jogs as a way to relax or take a break.

It's easy to believe that people's self-control fades over time, and they seem to have much less of it once they get fatigued. Remember what you bought the last time you were tired and hungry and went grocery shopping?

The dominant view has been that self-control is a limited resource, like energy. Our acts of restraint continually deplete the supply until there's none left and we are then powerless to control ourselves. Until you recharge, you won't have much self-control.

That's not so, says Michael Inzlicht, a psychology professor at the University of Toronto, Scarborough. What actually changes, Dr. Inzlicht says, is your degree of motivation.

“When people are ‘depleted’ or fatigued, they experience a change in motivational priorities such that they attend to and work less for things they feel obliged to do and attend to and work more for things they want to do — things they like doing.”

In other words, it is not that your self-control is completely gone, it is that you just can't quite access it, like a word that's on the tip of your tongue or a buried memory. You simply need something to jog your self-control, the way sounds, sights and scents can trigger a memory.

All it takes is a shift in attitude to access that buried self-control. Turn have-tos into want-tos.

Take the case of healthier eating: “If someone wants to eat healthier, they should think of the enjoyment that they can get from eating delicious, yet healthy, foods; in contrast, they should probably not frame their eating goal as something they feel obliged to do because their doctor or spouse is trying to convince them to do so,” Inzlicht suggests.

“The key is finding a way to want and like the goal that you are chasing. Some people do this naturally — think of the person who loves to run and jogs as a way to relax or take a break.”

It's still a good idea to steer clear of temptations when your energy levels are low. That's just tempting fate.

So if you feel like bad-mouthing yourself for failing to keep your New Year's resolutions, don't. Spend the energy finding a way to keep yourself focused on how good you will look and feel if you eat better, exercise more or go to bed earlier.

The paper appears in Trends in Cognitive Sciences.