This book is for explaining social phenomena. Many of its methods, theories, and examples come from economics, yet this book is not entirely about economics. If it were purely economics, it would have to use well-established economic theories to explain and analyze specific research subjects, and must discuss concepts and principles such as "supply", "demand", "price", "utility", "marginal" etc. Otherwise, it would be irresponsible to the readers. This book attempts to explain various social phenomena using scientific methods. Of course, economics is also scientific, but economics has already formed a fixed research pattern. Here we just want to tell the readers what lies behind many phenomena. Some parts of this book are "philosophical", some are "logical". What I want to say is that there are profound "scientific" reasons behind the social phenomena we see - in my view, these phenomena are backed by rationality and logic. If this book can bring some enlightenment to the readers, I will be satisfied. As long as the readers feel that they have gained more than the price they paid for this book, my conscience will be comforted, because I hope that writing this book and the readers' purchase of this book itself is a "cooperative game", rather than a "non-cooperative game".