When do characters in The Fault in Our Stars realize they are not as special as they thought they were?

There is a existential motif to this book. One involves the characters realizing the insignificance of their own lives in the grand scheme of things. Existentialist thought isn't big on the average teenager's things to ponder list. I think it might come somewhere after rechecking algebra homework. Does it really matter if one die's young of cancer if the world itself is meaningless? That sounds like something right out of an Albert Camus novel but it's actually teen fiction. I think a real moment of this type of "truth" comes about after Augustus dies and Hazel recalls her first encounter with him. She laments that the problem of life isn’t that it leads to oblivion, but that oblivion lacks any meaning at all.