Much of this is, indeed, rather over Ned's head. He's never questioned the fact that he does exist, that the universe exists, that the people he interacts with are real and not delusions. He can't imagine how frightening it must be, to doubt on such a fundamental level. The closest equivalent he can conjure up from his own experiences would be his early religious crisis, when he decided there was no God, no heaven and hell, no benevolent omnipotent consciousness looking down on him. That had been a paradigm shift that changed the way he looked at everything. But Ginsberg, from the sound of it, is stuck in that transitional phase, not able to take anything for granted.

He doesn't understand, but he does listen, and gradually Ginsberg's reasoning becomes more accessible to him. Questions of identity, he has dealt with. Not in the realm of nationality, as it seems to be in Ginsberg's case. But he feels on firmer ground responding to that

"I don't think so." He's careful to phrase it as an opinion - not making fun of Ginsberg for having doubts as to his own existence, but firm in his own conviction that Ginsberg is, in fact, real. He wonders if anyone had ever bothered to give him even that, or if they had scoffed and spouted some variation on of course you're real. "The only way that would make you not real is if you believe someone's past is the key to who they are, and I don't think that. Not the only one, anyway. Maybe... maybe another way to look at it is: even if you don't know what you are, and can never know for certain, that means you get to decide who you want to be."

He knows it sounds cheesy, but it's what he's always done. He's focused that old anxiety over what kind of monster he must be into efforts to redefine himself, to build scaffolds and structures around that emptiness, around that unanswered question.