That characterization of "a man who knows himself" rings false to my ears. It describes someone with unexamined self-confidence, not someone who truly has self-knowledge. The deeper you go into trying to know yourself, the more you realize that it's hard to pin down the object of that knowledge, and hard to distinguish the self you're supposed to know from the world, or life. You'll start to become more aware of your inseparability from the others on whom you depend, and of just how fluid your own nature can be and how it slips free from your grasp each time you convince yourself you've got it. For a while at least, uncertainty increases with self-knowledge. Thus true self knowledge is more an ongoing practice than a project that gets completed, and a project that encourages humility and empathy more than the kind of clueless arrogance described here.