It is a psychological law ...

It is a psychological law that whatever we desire to accomplish we must impress upon the subjective or subconscious mind; that is, we must register a vow with ourselves, we must make our resolution with vigor, with faith that we can do the thing we want to do; we must register our conviction with such intensity that the great creative forces within us will tend to realize them. Our impressions will become expressions just in proportion to the vigor with which we register our vows to accomplish our ambitions, to make our visions realities.
 Orison S. Marden

Quotes from the same author

The ability to talk well is to a man what cutting and polishing are to the rough diamond. The grinding does not add anything to the diamond. It merely reveals its wealth.
 Orison S. Marden
Work kills no one, but worry has killed multitudes… Worry not only saps vitality and wastes energy, but it also seriously affects the quality of one's work. It cuts down ability. A man cannot get the highest quality of efficiency into his work when his mind is troubled. The mental faculties must have perfect freedom before they will give out their best. A troubled brain cannot think clearly, vigorously, and logically.
 Orison S. Marden
The moment a man ceases to progress, to grow higher, wider and deeper, then his life becomes stagnant.
 Orison S. Marden
The size and quality of your achievement will depend largely upon what sort of image you have of yourself at your best.
 Orison S. Marden
Real happiness is so simple that most people do not recognize it.  They think it comes from doing something on a big scale, from a big fortune, or from some great achievement, when, in fact, it is derived from the simplest, the quietest, the most unpretentious things in the world.
 Orison S. Marden