Where are the meaningful boundaries in reality? If there are none - if boundaries are a construction of the mind - then there is no difference between "self" and "not-self", or between "the perceiver" and "the perceived".
In this way, mystics claim that "all is one".
It's a beautiful idea, though I don't think it's quite accurate. Regardless, it needs to be rationally defended and grappled with.
All is One: The Logical Case for Mysticism