This is the first chapter of Part I, which covers the relevant psychology. I summarize research showing that self-control is “a significant predictor of school and work achievement, income and socioeconomic status, financial planning and struggle, physical health, eating and weight-related behavior, substance abuse, decision-making, relationships and interpersonal skills, ability to deal with anger, frustration, and stress, and – last but not least –criminal offenses.” The correlation between these outcomes and the capacity for self-control is considerable, sometimes even outstripping the correlation with intelligence. The chapter also shows that having good self-control is not just a matter of volition, but has all the characteristics of a personality trait. Some people are better at self-control than others, with the basic capacity for self-control largely determined by genes and early upbringing.