What is human nature like? Why do we act as we do? How can we make ourselves different? How can we make others different? How can we make ourselves more efficient? How can we make our lives more worth while? This book is a manual intended to help young people to obtain such knowledge of human nature as will enable them to answer these questions. I have not attempted to write a complete text on psychology. There are already many such books, and good ones too. I have selected for treatment only such topics as young students can study with interest and profit. I have tried to keep in mind all the time the practical worth of the matters discussed, and the ability and experience of the intended readers.