Drawing on current research, this book demonstrates that there are rational reasons for why certain actions should reasonably not be considered duties despite their moral value. Would you do something unpleasant or dangerous you are not obliged to, simply because it would benefit others? “I won't do this because I don't have to”. This argument of supererogation can be used to reject overly demanding moral expectations. Yet, the argument is not always equally convincing. For instance, refusing to donate a kidney is morally accepted. Refusing a favor to a friend, however, seems indecent. Perhaps supererogatory acts do not exist at all? This book offers a refined framework for understanding the boundaries of moral duty. It is of interest to students and scholars of moral philosophy, applied ethics and meta ethics.