Liane Moriarty is truly one of my favorite writers. In all of her books, including this one, she has a way of creating characters who are hilarious even amid devastation, who are extremely real, who are likeable even when they do things I don't like. 
 Her novels also normally have a definable theme that permeates the entire story, along with the "typical" themes of women's fiction (love, family, and friendships). This one is all about memories, and not just the ones Alice lost when she hit her head. It's about how the memories we retain make us who we are. This is, of course, most true when Alice loses 10 years of memories and reverts to her younger self's personality, but it's not only that. The memories each character has about the death of Alice and Elisabeth's father shapes how she feels: Alice remembers how kind her big sister was when telling her about his death, but Elisabeth doesn't recall telling Alice at all; their mother remembers Alice's attachment to her dad's sweater, but Alice doesn't. There are incidents like that all throughout the book, where characters remember situations from different angles, and the angles in turn shape their feelings about the incident and the other people involved. 
 It all comes down to the idea that memories are not inert; they are a powerful force, shaping our lives and relationships. This idea is handled gracefully, and the ending of the story is satisfying.