Ten-year-old Isabelle and her eight-year-old cousin Isabella have a few tips for living life. Well, maybe more than a few. Begun as a guide for Isabelle’s younger sister, the girls’ list quickly grew, and soon more than 150 rules filled a secret notebook. Some rules are simple: “Recycle.” “Eat whatever your mom makes for dinner and don’t complain.” Others are practical: “Go to sleep early if you have soccer practice in the morning.” Others are sweet: “Protect each other.” And others are downright hilarious: “Color on paper, not on people.” “Don’t bite the dentist.” When Isabelle and Isabella lost their handwritten list of rules in a store, they feared it was gone forever. But after a clerk found their notebook and posted about it on Facebook, Isabelle and Isabella became overnight sensations—the staff of said, “Everyone here wants a copy of this. This is going to be a bestseller!” Because after all, who doesn’t need a little help navigating their way through life, at any age?