When we read, another person thinks for us: we merely repeat his mental process. In learning to write, the pupil goes over with his pen what the teacher has outlined in pencil: so in reading; the greater part of the work of thought is already done for us. This is why it relieves us to take up a book after being occupied with our own thoughts. And in reading, the mind is, in fact, only the playground of another’s thoughts. So it comes about that if anyone spends almost the whole day in reading, and by way of relaxation devotes the intervals to some thoughtless pastime, he gradually loses the capacity for thinking; just as the man who always rides, at last forgets how to walk. This is the case with many learned persons: they have read themselves stupid.

Arthur Schopenhauer