The life course is shaped by the interaction of cultural and social structural features with physical and psychological attributes of the individual and by the commitments and purposive efforts of the individual. In modern society, rationality and functionality have replaced tradition as determinants of individual choices in the transition to adulthood. Adolescent competence should lead to thinking through career and marital choices and inhibiting tendencies to make unwise choices. Therefore, competent adolescents should have more stable careers and marriages, and, because they will more often be rewarded for their attributes than will less competent ones, they should experience less personality change over the adult years. These hypotheses are largely confirmed with data from a longitudinal cohort studied for more than 50 years.