The key to the mind is the knowledge of life. There is only one real key. It is learnt in one moment; but the nature of life is such that we forget. The key to the mind is the knowledge of life; in other words, it is the psychology of life, and there is rarely a person who knows the psychology of life profoundly. Man has the faculty of knowing, but he is so absorbed in life that he does not give time to practice the psychology of Life which is more precious than anything in the world.