This is why we are consciously relieved when we turn to reading after being occupied with our own thoughts. But, in reading, our head is, however, really only the arena of some one else’s thoughts. And so it happens that the person who reads a great deal—that is to say, almost the whole day, and recreates himself by spending the intervals in thoughtless diversion, gradually loses the ability to think for himself; just as a man who is always riding at last forgets how to walk. Such, however, is the case with many men of learning: they have read themselves stupid. For to read in every spare moment, and to read constantly, is more paralysing to the mind than constant manual work, which, at any rate, allows one to follow one’s own thoughts. Just as a spring, through the continual pressure of a foreign body, at last loses its elasticity, so does the mind if it has another person’s thoughts continually forced upon it. And just as one spoils the stomach by overfeeding and thereby impairs the whole body, so can one overload and choke the mind by giving it too much nourishment. For the more one reads the fewer are the traces left of what one has read; the mind is like a tablet that has been written over and over. Hence it is impossible to reflect; and it is only by reflection that one can assimilate what one has read if one reads straight ahead without pondering over it later, what has been read does not take root, but is for the most part lost.
Arthur Schopenhauer, «On Reading and Books.»