Man is a growth by law, and not a creation by artifice, and cause and effect is as absolute and undeviating in the hidden realm of thought as in the world of visible and material things. A noble and Godlike character is not a thing of favour or chance, but is the natural result of continued effort in right thinking, the effect of long-cherished association with Godlike thoughts. An ignoble and bestial character, by the same process, is the result of the continued harbouring of grovelling thoughts.
Man is made or unmade by himself; in the armoury of thought he forges the weapons by which he destroys himself; he also fashions the tools with which he builds for himself heavenly mansions of joy and strength and peace. By the right choice and true application of thought, man ascends to the Divine Perfection; by the abuse and wrong application of thought, he descends below the level of the beast. Between these two extremes are all the grades of character, and man is their maker and master.
~ James Allen – As A Man Thinketh (1903)