No two human beings are alike; it's a question of identity. And what is identity? The cognitive system arisin' from the aggregate memories of that individual's past experiences. The layman's word for this is the mind. Not two human beings have the same mind. At the same time, human beings have almost no grasp of their own cognitive systems. I don't, you don't, nobody does. All we know—or think we know—is but a fraction of the whole cake. A mere tip of the icing.