I have always been deeply interested in ethical issues in economics. Not long ago, when Xu Chongzheng sent a proof copy of his book, Comprehensive Human Development and Social Economy: An Introduction to Ethics, and asked me to write a preface for the book, I agreed. But what to write about? On a second thought, I would like to address the issues of the relationship between social mobility and comprehensive human development, and the ethical judgment on social mobility. We often encounter these two issues but seldom talk about them in our lives.