"A library may be very large; but if it is in disorder, it is not so useful as one that is small but well arranged. In the same way, a man may have a great mass of knowledge, but if he has not worked it up by thinking it over for himself, it has much less value than a far smaller amount which he has thoroughly pondered. For it is only when a man looks at his knowledge from all sides, and combines the things he knows by comparing truth with truth, that he obtains a complete hold over it and gets it into his power. A man cannot turn over anything in his mind unless he knows it; he should, therefore, learn something; but it is only when he has turned it over that he can be said to know it.
Reading and learning are things that anyone can do of his own free will; but not so thinking. Thinking must be kindled, like a fire by a draught; it must be sustained by some interest in the matter in hand. This interest may be of purely objective kind, or merely subjective. The latter comes into play only in things that concern us personally. Objective interest is confined to heads that think by nature; to whom thinking is as natural as breathing; and they are very rare. This is why most men of learning show so little of it."
…excerpt from: On Thinking For Oneself by Arthur Schopenhauer