The test of bringing thoughts and theories, intuitions and revelations, to action is a means not only of expressing them but also of evaluating them. It is only by doing this, by bringing them face to face with the facts of life that he can learn what they are really worth or how they should really have been executed. Even though the opportunity to act wisely has been lost, the knowledge has been gained. Even though he may never be able to make use of it again in this lifetime, it remains in his mind and will enrich his later incarnations. Experience of the world, however studded with faults and mistakes it may be, must always complement understanding of life if he is to accomplish his fullest development. The abstract is man's left arm, the concrete is his right one. As he applies his ideas directly to the outward life, they become fruitful. Thus he is able to see for himself whether the fruit is good or bad, and to judge the tree accordingly.
-- Notebooks Category 13: Human Experience > Chapter 1: Situation > # 96