Adam Smith regarded The Theory of Moral Sentiments as far more important than his most famous work The Wealth of Nations. He devoted most of his life to revising and improving The Theory of Moral Sentiments. In this book, beginning with human sympathy, Smith comprehensively and systematically discusses a set of concepts, such as good and evil, justice, beneficence, prudence, and self-denial. He believed that sympathy is the origin of all ethics such as justice, beneficence, and self-denial.