Basil of Caesarea

In truth, to know oneself seems to be the hardest of all things. Not only our eye, which observes external objects, does not use the sense of sight on itself, but even our mind, which contemplates intently another's sin, is slow in the recognition of its own defects. Therefore, even at present our speech, after eagerly investigating matters pertaining to others, is slow and hesitant in the examination of our own nature. Yet, it is not possible for one, intelligently examining himself, to learn to know God better from the heavens and earth than from our own constitution, as the prophet says, "Your knowledge is become wonderful from myself"; that is, having carefully observed myself, I have understood the superabundance of wisdom in you.