'The Investment of Influence: A Study of Social Sympathy and Service' is a philosophical book that delves into social influence from a practical perspective. It was written by Newell Dwight Hillis, a Congregationalist minister, writer, and philosopher from Brooklyn. In his preface, he discusses his reasons for wanting to write this book: “The glory of our fathers was their emphasis on the principle of self-care and self-culture. Finding that he who first made the most of himself was best fitted to make something of others, the teachers of yesterday unceasingly plied men with motives of personal responsibility. Influenced by the former generation, our age has organized the principle of individualism into its home, its school, its market-place and forum. Because of the increase in gold, books, travel and personal luxuries, some now feel that selfness is beginning to degenerate into selfishness. The time, therefore, seems to have fully come when the principle of self-care should receive its complement through the principle of care for others. These chapters assert the debt of wealth to poverty, the debt of wisdom to ignorance, the debt of strength to weakness.”