"But you are. Your purpose can be whatever you want it to be. Mine isn't." It's just said in a matter of fact tone of voice. There's so much to 9S, he can find a new purpose and it can be so many different things.

But it's different with Cole. He's a spirit, defined by one essence so strongly that it's a cornerstone of his being. He lost his purpose, though it was something different, but then discovered what it was and how to do it. He's compassion. He heals. And he can't be any other way.

"Now that I know what I am, I couldn't be anything else."