social scientists Lykken and Tellegen starkly suggest, ‘trying to be happier is as futile as trying to be taller.’ Thus, the swimmer’s body illusion is also a self-illusion. When these optimists write self-help books, the illusion can become treacherous. That’s why it’s important to give a wide berth to tips and advice from self-help authors. For billions of people, these pieces of advice are unlikely to help. But because the unhappy don’t write self-help books about their failures, this fact remains hidden.