She was utterly unaffected by their situation, but Lucy was living her worst nightmare — frozen on the bridge, inches away from the railing and the terrifying drop to the water.
-- Narrator (Chapter 1)

Importance: The author makes a point to present contrasting behavior between Lucy, who almost has a panic attack on the bridge, and Brynn, who is completely unaffected by their situation. He makes it appear that Lucy is the one who is about to have some sort of psychotic break when it is really Brynn who will panic and kill herself. The reader does not know at the time that Todd triggers the panic attack and that he set up the attack during sessions of hypnosis and drugs just like Frankie conducted to remove bad memories.

We were stuck in traffic. I was scared because of the bridge, but Brynn was fine. Joking, singing. Totally normal. And then she turned psycho. It...
-- Lucy (Chapter 2)