Walking to class, Cath couldn’t shake the feeling that she was pretending to be a college student in a coming-of-age movie.
-- Narrator (Chapter 2 paragraph 14)

Importance: Even though Cath isn’t in the coming-of-age movie she imagines she is in, she is in a coming-of-age book. Her story is very much one of coming-of-age and facing one’s demons.

And Wren didn’t take up nearly as much space as Reagan did. Figurative space. Head space.
-- Narrator (Chapter 3 paragraph 5)

Importance: Cath refers to the feeling that there is so much of Reagan and her personality that Cath doesn’t even have room to think when she is in the room. Cath had never gotten this feeling with her sister, Wren, in the room with her.

It’s not just that.… I don’t like new places. New situations. There’ll be all those people, and I won’t know where to sit — I don’t want to go...
-- Cath (Chapter 4 paragraph 84)