It seems to be the special peculiarity of human beings that they reflect: they think about thinking and know that they know. This, like other feedback systems, may lead to vicious circles and confusions if improperly managed, but self-awareness makes human experience resonant. It imparts that simultaneous "echo" to all that we think and feel as the box of a violin reverberates with the sound of the strings. It gives depth and volume to what would otherwise be shallow and flat.