Because One by One is told through two first-person perspectives, all the knowledge the reader receives is filtered through Erin and Liz’s experiences. Both women have very intense memories that emerge at different points in the novel, and these flashbacks inform why they act the way they do, comprising a motif about past memories shaping present circumstances.

Erin’s memories center around the avalanche that killed her brother and boyfriend. These memories do not affect her day-to-day life, since she focused exclusively on her work and only rarely slips into her own past. However, the arrival of the avalanche that buries Chalet Perce-Neige triggers these memories in a way she cannot control. She notes, “for a moment I thought it was some kind of flashback, like PTSD” (110). Still, she does not share her experience with anyone until late in the novel, after Topher verbalizes the memories that she tries so hard to suppress. She then relives the traumatic experience twice: first with Danny in the staff quarters, and then with Liz after the others leave to seek help. It is not until the second time Erin tells her story that she reveals a key piece of information—that she was the one who suggested that her group ski off-piste the day of the avalanche.