Concentration does not, as popularly supposed, mean keeping the mind fastened on one object or idea or in one place. It consists in having a problem or purpose constantly before one. It means keeping our thought moving toward one desired end. Concentration is often regarded as intense or focused attention. But the fact is that all attention is focused attention. Psychologists are fairly well agreed that we can attend to only one thing at a time. Mind wandering, and so-called distributed attention, is really attention directed first to one thing, then to another, then to another; or first to one thing, then to another, and then back again to the original object, resting but a few moments on each idea. Concentration may best be defined as prolonged or sustained attention. It means keeping the mind on one subject or problem for a relatively long period, or at least continually reverting to some problem whenever one’s thoughts momentarily leave it. Having decided just what we mean by concentration, our next step is to inquire whether concentration is worth while. The reader may smile at this question or he may be shocked, according to his temperament. But if most men were so convinced that concentration is such an unquestionable virtue, they would practice it a little more. At least they would make greater efforts to practice it than they do at present. The truth is that concentration, _per se_, is of little value. The value of concentration depends almost entirely on the subject concentrated on. Almost any one will agree that even were a man to allow his mind to dwell now on one important problem and now on another, without stopping a very appreciable time at any, he might nevertheless be improving his time far more than a man who concentrated continually on some insignificant and inconsequential question. But of course this is not really an argument against concentration. It has no application when you concentrate on the proper subject. For if you start to concentrate on some question which you have decided is really important, you should keep at it, allowing no deviation. It may be that during the course of your thought associations will be aroused which will suggest or bear upon important problems, problems more important perhaps than the one you originally started to concentrate on. But if you immediately abandoned every problem you started to think of, whenever you came across one which you imagined was just as important, you would probably never really solve any big question.