“Look at the sea, not at the waves.”
The sea and the waves cannot be separated, they are the same. But because we have attachments created by illusion, we differentiate them from each other. Standing on the shore we say, “Oh, look at those waves, how big!” Others say, “Look at this big sea!”
The person who could consider this whole universe as an illusion would be the self-realized person, who has become one with his essence, with his essential self.