Here’s the part where I should probably mention that Cassie and I are sperm donor babies. So that’s a thing in my life: that tiny niggling idea that everyone I meet might actually be my half sibling.
-- Narrator (Chapter 1)

Importance: Once aspect of Molly’s modern life is that she is the daughter of a homosexual couple. She was conceived by a sperm donor and does not know what that man looked like so it is always disconcerting to her when people tell her that she looks like someone familiar. Albertalli uses sentences like this one to sneak in information about Molly’s lifestyle and family structure.

This is a fundamental difference between us. I was basically born knowing how to casually stalk people on social media. But I guess Cassie’s more the kind of person who gets casually stalked.
-- Narrator (Chapter 2)

Importance: Molly points out several differences between herself and her sister...