The mind itself is the medium of all knowledge, and the quality of that knowledge depends upon the quality of the mind. A dull mind will produce dull knowledge; a penetrating mind will penetrate to the heart of things.
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It is not when truth is dirty, but when it is shallow, that the lover of knowledge is reluctant to wade into its waters.
Friedrich Nietzsche — Thus Spoke Zarathustra
The multitude of men agree in this: that they equate thinking with reading, and spare themselves the trouble of thinking, because they are able to read. They thus very much resemble those who to escape from want have sold their heritage, and now hope to live by their wages from those who have acquired it.
Arthur Schopenhauer — Parerga and Paralipomena
A fact is not a truth until you love it.
John Keats — Letters of John Keats