"Hans: [to Snake] Are you familiar with the term "doppelganger"? Everyone has two personalities in them. One of them a persona for everyday public life, and the other the exact opposite. The personality lurking in one's subconscious is referred to as the "Shadow" in psychological terms. The Shadow negates its symmetrical opposite, the "Light" persona, and in some cases grows to the same level. If it manages to grow large enough, it takes on its own shape, separates from the body, and can walk around on its own. And that, my friend, is why we're both here."