Conviction of Sin
The beginning of John Calvin's Institutes of the Christian Religion is a goldmine on epistemology and anthropology. The intrinsic nature of knowledge of God and knowledge of man for Calvin is almost like a dance—the two come together and in each we understand the other better. This is particularly useful in understanding how we attain knowledge of our own sinfulness.
Man's incompetence is not an anthropological judgment drawn from the knowledge of man in himself (126)
This articulation is delivered at the uring of Calvin's catechism. But it just as well might have come from his introductory chapter of the Institutes:
It is evident that man never attains to a true self-knowledge until he has previously contemplated the face of God, and come down after such contemplation to look into himself. For (such is our innate pride) we always seem to ourselves just, and upright, and wise, and holy, until we are convinced, by clear evidence, of our injustice, vileness, folly, and impurity. Convinced, however, we are not, if we look to ourselves only, and not to the Lord also—He being the only standard by the application of which this conviction can be produced. For, since we are all naturally prone to hypocrisy, any empty semblance of righteousness is quite enough to satisfy us instead of righteousness itself. And since nothing appears within us or around us that is not tainted with very great impurity, so long as we keep our mind within the confines of human pollution, anything which is in some small degree less defiled delights us as if it were most pure just as an eye, to which nothing but black had been previously presented, deems an object of a whitish, or even of a brownish hue, to be perfectly white. (Inst, I.I.II)
Contra some popular opinions, conviction of one's sinfulness is not native in the sense that man without knowledge of God could obtain it. This knowledge of God is a Divine gift and grace. It is to Him and His Son that we must continue to look to receive knowledge of our sinfulness and the subsequent forgiveness of those sins.