One becomes Two
Looking into a mirror, what does one see? A mirror limits the view to a lesser dimension. It is not possible to see outside of all that is, and the position of the mirror at best reflects a lesser dimension of the whole.
Thus, completeness and wholeness is compromised. It exists but is not apparent in the reflection. The mirror only reflects that which most prominent and visible before it. Thus, duality cannot be a mirror for the One.