The range of purposes on which man can successfully direct his mind, through concentration, is limitless. Every living creature below man concentrates its efforts on but two ends, reproduction and food.

Other physical manifestations of the law of concentration are seen in the sun that sets and rises with uninterrupted regularity—water that flows downhill in response to the law of gravitation—the seasons of the year which inevitably come—and every living thing, including man, reproducing itself after its kind.
Here is evidence that the law of concentration is not man-made, because none of man’s efforts has ever interrupted any of these manifestations of the Creator’s purpose.
Determine what you want most from life. Adopt that as your definite major purpose. Make the start toward your goal right where you stand. When you come to those uphill pulls where the going is hard, back it with all the enthusiasm at your command, and lo! You will find yourself in the right path.
You will be on the “success beam” that will carry you unerringly to the object of your aims and purposes. Try it! It works.
Source: The Science of Success. Napoleon Hill. Penguin. Release date Sept. 4, 2014. Pgs. 210 – 211.
About Napoleon Hill:
Napoleon Hill was born in 1883 in a one-room cabin on the Pound River in Wise County, Virginia. He began his writing career at age 13 as a “mountain reporter” for small town newspapers and went on to become America’s most beloved motivational author. Hill passed away in November 1970 after a long and successful career writing, teaching, and lecturing about the principles of success. His work stands as a monument to individual achievement and is the cornerstone of modern motivation. His book, Think and Grow Rich, is the all time bestseller in the field. Hill established the Foundation as a nonprofit educational institution whose mission is to perpetuate his philosophy of leadership, self-motivation, and individual achievement. His books, audio cassettes, videotapes, and other motivational products are made available to you as a service of the Foundation so that you may build your own library of personal achievement materials… and help you acquire financial wealth and the true riches of life.