Some people cannot endure planning their reading in this manner. It grates on them to think they are tied down to any sort of program; it seems to deprive them of the advantages of spontaneous interest. Well, if you cannot plan your reading prospectively, at least plan it retrospectively. If you cannot keep a list of books you _intend_ to read, at least keep a list of books you _have_ read. Refer to this from time to time. See whether you have been reading uniformly good literature. See whether you have been reading too much on one topic and not enough on another, and what topics you have been long neglecting. But at best this method is a poor substitute for planning your reading prospectively. We should plan not only with regard to topics and subjects, but with regard to authors. Obviously if two men of equal ability both study the same subject, one will get more out of his study than the other if he reads authors who treat the subject on a deeper plane—provided of course he understands them. Whether consciously or not, we tend to imitate the authors we read. If we read shallow books we are forced, while reading them, to do shallow thinking. Our plane of thought tends toward the plane of thought of the authors we study; we acquire either habits of careful critical thinking, or of dogmatic lack of thinking. This emphasizes the importance of reading the best books, and _only_ the best books. Our plane of thinking is determined not alone by the good books we read, but by all the books we read; it tends toward the _average_. Most men imagine that when they read a good book they get a certain amount of good out of it, and that this good will stay with them undiminished. Provided they read a certain number of serious books, they see no reason why they should not read any number of superficial or useless books, or any amount of ephemeral magazine or newspaper literature. They expect the serious reading to benefit them. They do not expect the shallow reading to harm them. This is just as if they were to buy and eat unnutritious and indigestible food, and excuse themselves on the ground that they ate nourishing and digestible food along with it.