There are two parts to concentrating. One is to get rid of extraneous thoughts, the other is to focus on the task at hand. Getting rid of interfering thoughts, ranging from annoying “ear worm” songs to recurrent thoughts of personal stresses or family problems, is not as easy as simply telling yourself not to think about them. Research suggests that if something is preying on your mind, you may do best to concede it to some degree. One approach is to go ahead and dwell on it for a short, fixed time before going back to work. Another approach is to postpone the unwanted thought: “I’ll deal with that problem this evening at 7.”
Focusing on the problem requires sustaining your attention. This is an issue for self-control and willpower. Willpower is tied to the basic energy supplies that your brain and body use. The chemicals that enable your brain cells to fire are made from the glucose in your bloodstream. All manner of self-control—including controlling your emotions—draws on the same stock of energy. Making decisions also depletes glucose and thus willpower, so after a series of decisions you will be less able to concentrate (or to resist temptation). To some extent you can replenish your willpower by getting rest or just eating something—normally it takes about 15 minutes for nutrients to be available as brain fuel. And trying to concentrate while sick will divert glucose from your immune system, impairing your body’s ability to fight the illness. Sometimes the most efficient thing is simply to go to bed.