Basically, we found that both sides of the self-control debate were right.
For a while, most people could focus on the boring bull's-eye. But they'd hit a fatigue point. After that, if subjects hung in there and still stuck with the task, they ended up exhausting their self-control "battery." We could see this by looking at how many impulse buys they made in the second half of the study. If they'd pushed past the fatigue threshold in the previous task, they showed less self-control and ended up making more impulsive purchases. This pattern was shown in both what they "bought" in our experiment and also in the brain: The prefrontal cortex showed patterns indicative of impulse-buying behavior.
On the other hand, subjects who eased off once they'd reached the fatigue threshold had a different experience. They remained in the "snowball" stage of self-control – they practiced the skill a bit, but didn't overdo it to the point of exhaustion. In the next task, their brains didn't exhibit the typical impulse-buying activity patterns. Exercising self-control on the bull's-eye task, but not overdoing it, led to more self-control in our second task. These subjects did better at controlling impulse purchases than the other group of subjects who didn't have the initial bull's-eye-watching session that turned out to rev up self-control.
Our study suggests that self-control has the qualities of both snowball and battery: Exhibiting self-control once makes it easier to do so again a short time later, but overdoing it initially makes us more likely to give up altogether.
How to make it past February 1
Our new understanding of self-control provides lessons for sticking with those New Year's resolutions.
First, remember that slow and steady is best. If you want to get fit, start by walking around the block, not running five miles. Achieve enough to stay motivated, but don't overdo it to the point of frustration. Don't burn out your self-control battery.
Second, remember that small acts of self-control build over time. Instead of drastically cutting all carbs or sugar out of your diet, consider giving up just one piece of bread or one can of soda per day. Over time, consuming fewer calories per day will result in gradual weight loss.
And finally, realize that little acts of self-control in one area will improve your self-control in other areas. Getting traction with a healthier diet, for example, will increase your confidence and motivation to achieve another goal. As the self-control snowball gains some momentum, you'll get better and better at sticking to your objectives.
A more apt metaphor for our new understanding of self control is that it's like a muscle. You can overdo it and exhaust it if you overexert yourself beyond your capabilities. But with consistent training it can get stronger and stronger.