The air-brake is probably one of the most valuable inventions ever applied to the railroad industry, and yet George Westinghouse, its inventor, found it impossible even to give it away to railroad presidents until he had learned how to sell it. The telephone, perhaps the greatest convenience, luxury, and time and money saver of modern times, would have remained a scientific toy unless the most astute and vigorous methods of persuasion had been used to insure its almost universal adoption and use. We have seen that Elias Howe built the first sewing machine so well that its fundamentals have never been improved upon, and yet, despite his most strenuous efforts and the efforts of his friends and associates, it remained a mere mechanical curiosity until he had learned how to persuade others to use it. MUTUALITY OF ALL HUMAN INTERESTS A.F. Sheldon has said, "Salesmanship is not conquest, but co-operation." Salesmanship is only the commercial name for persuasion, therefore Mr. Sheldon has uttered a great truth. Human interests do not clash, however much they may appear to. All human interests are mutual. John D. Rockefeller did not amass a fortune by making others poor. On the contrary, in the building up of his hundreds of millions, he increased the wealth of others by billions. The theory that there is not enough wealth to go around, and that if one man has a great deal of money others must therefore have too little, is a vicious and dangerous fallacy. The resources of the universe are infinite. The possibilities of humanity are unlimited. The interests of all lie, fundamentally, in the greater and greater development of the latent possibilities in all men and the more and more efficient exploitation and conservation of the resources of the universe. This is philosophic. It is a generalization. It is a statement of facts so tremendous in their scope and so deep in their significance that it is difficult to make a connection between them and the practical details of every-day life. PERSUASION REVEALS MUTUALITY OF INTERESTS The very fact that human intercourse, in every aspect of its activity, rests upon persuasion is an indication that all interests are mutual. The persuader teaches the persuaded that their interest coincide. Take a practical example: Salesmen have declared to us that life insurance policies are the most difficult of all specialties to sell. Yet, in nine cases out of ten, policyholders will agree that their benefits far exceed those derived by the salesmen who persuade them to purchase. The life insurance salesman is not attempting to hoodwink, hypnotize, cajole, or browbeat his client in a case where their interests clash, but simply, by skilful setting forth of facts and appeals to the feelings, to persuade his client to act in his own interest.