Chapter 15 defends the critical implications of chapter 13 against the arguments that arbitrage and experiencing the costs of irrational behavior justify dismissing anomalous experimental results, such as those concerning preference reversals. The chapter then draws out some of the implications for the practice of economics of its philosophical conclusions, drawing on the work of George Akerlof and others who have studied conditional altruism and defended its importance. Chapter 15 also defends the legitimacy of the methodological preaching in this book against criticisms such as those voiced most compellingly by Deirdre McCloskey.