In my opinion, the great philosopher David Hume understood why human self-understanding was forever beyond our reach. It is not a coincidence that he always expressed himself with irony, for the deepest irony possible is that of the existence of a creature, Man, who forever seeks something that is beyond his understanding.
Hume was simultaneously a figure of the enlightenment and the anti-enlightenment. He saw that reason and consideration of the evidence are all that a rational man can rely upon, yet they are eternally insufficient for Man as he is situated. In short, there cannot be such a thing as the wholly rational man. Reason, he said, is the slave of the passions; and in addition, no statement of value follows logically from any statement of fact. But we cannot live without evaluations.
Ergo, self-understanding is not around the corner and never will be. We shall never be able seamlessly to join knowledge and action. To which I add, not in any religious sense: thank God.
