Our existence as human beings is conditioned, and at times even dominated, by circumstances. Often we should like to remold these, but to do so requires control, and control indicates the need for power, and power depends upon knowledge. This is the justification of philosophy. When we understand its doctrines aright, that mind constructs its experience, its environment, its world, we understand the implication that an amendment in our environment can come only through amendment in our thinking. Thought is creative, and we are continually building both ourselves and our environment by the characteristics and qualities of our thoughts.
-- Notebooks Category 21: Mentalism > Chapter 5: The Key To the Spiritual World > # 45