To tell if you are going to get the happiest ending, select the answer to see if the screen sparkles briefly. It is recommended to write down your answer each time you choose since it is only an A/B choice. That way if you choose the one that doesn't sparkle the next time you will have the correct answer. Getting the Happiest Ending is based on how many correct (sparkly) answers you choose. There are 2 'questions' for every chapter except the very last one so there are 26 answers you have to choose.