Secrets are complicated and keeping them will always have repurcussions. In the case of what happened to Aaron, the secret that he kept with Luke about Ellie completely changed his life and his father's life. It effectively ruined his relationship with his father and completely changed the course of their lives. If he hadn't lied to his father and come clean about where he actually was that day, things might have turned out differently. If Luke and Gretchen had told the truth, Ellie's father might have been revealed as the murderer a lot sooner. In the case of Gretchen keeping Lachie's father a secret, that is a lot less major, but could have repurcussions down the road for Lachie at least. In his case, if his Luke is the father, than he has grandparents who he could be having a relationship with and he's not. There are so many secrets in this book, I could go on all day. Some secrets are less harmful than others, but I think they are always harmful to someone.