Here’s an interesting quote by Charles Haanel:

“If you concentrate upon the thoughts given; if you give them your entire attention, you will find a world of meaning in each sentence, and will attract to yourself other thoughts in harmony with them, and you will soon grasp the full significance of the vital knowledge upon which you are concentrating.

Knowledge does not apply itself; we as individuals must make the application, and the application consists in fertilizing the thought with a living purpose.

The time and thought which most persons waste in aimless effort would accomplish wonders if properly directed with some special object in view. In order to do this, it is necessary to centre your mental force upon a specific thought and hold it there, to the exclusion of all other thoughts. If you have ever looked through the focussing screen of a camera, you found that when the object was not in focus, the impression was indistinct and possibly blurred, but when the proper focus was obtained the picture was clear and distinct.

This illustrates the power of concentration. Unless you can concentrate upon the object which you have in view, you will have but a hazy, indifferent, vague, indistinct and blurred outline of your ideal and the results will be in accordance with your mental picture.”