As a Man Thinketh by James Allen

Only by much searching and mining are gold and diamonds obtained, and man can find every truth connected with his being, if he will dig deep into the mine of his soul. That he is the maker of his character, the molder of his life, and the builder of his destiny, he may unerringly prove, if he will watch, control, and alter his thoughts, tracing their effects upon himself, upon others and upon his life and circumstances, linking cause and effect by patient practice and investigation. And utilizing his every experience, even the most trivial, everyday occurrence, as a means of obtaining that knowledge of himself which is understanding, wisdom, power. In this direction is the law of absolute that "He that seeketh findeth; and to him that knocketh it shall be opened." For only by patience, practice, and ceaseless importunity can a man enter the door of the temple of knowledge.