Answer:
There is someone, and there is always another, for without the other, there wouldn't be one
Two little holes in the side of a hill. Just as you come to the cherry-red mill.
I appear in the morning. But am always there. You can never see me. Though I am everywhere. By night I am gone, though I sometimes never was. Nothing can defeat me. But I am easily gone.
My second is performed by my first, and it is thought a thief by the marks of my whole might be caught.
He has one and a person has two. A citizen has three. And a human being has four. A personality has five. And an inhabitant of earth has six.
What covers its face with its hands, speaks no language, yet most known what it's saying?