When we read someone else thinks for us: we merely repeat his mental process. […] Accordingly in reading we are for the most part absolved of the work of thinking. […] It stems from this that whoever reads very much and almost the whole day, but in between recovers by thoughtless pastime, gradually loses the ability to think on his own — as someone who always rides forgets in the end how to walk. […] For constant reading immediately taken up again in every free moment is even more mentally paralysing than constant manual labour, since in the latter we can still muse about our own thoughts. But just as a coiled spring finally loses its elasticity through the sustained pressure of a foreign body, so too the mind through the constant force of other people’s thoughts.
Schopenhauer, A. (1851). On reading and books.