Books, too, serve as guides if they are properly used, that is, if their limitations are recognized and if their authors' limitations are acknowledged. In the first case it is the intellect's own inability to transcend thought that stops it from realizing truth. In the second case it is the evolutionary status of the man's ego, and the accuracy of his attitudes--themselves victims or controllers of his emotions, passions--which matter. For if his mind cannot register the impact of truth, because of the blockage set up partially or even all around him, the author's work will reflect his ignorance. He cannot teach what he does not know; his own mental obscurity can lead only to the reader's obscurity. Yet such is the deceptiveness of thought, that a wrong or false idea may be received and held in the mind under the belief that it is a right or true one.
-- Notebooks Category 1: Overview of the Quest > Chapter 6: Student-Teacher > # 98