From the brilliant Richard Florida in CityLab - The Self-Confident City (Big cities are a powerful draw for confident people, who in turn benefit the most form their opportunities and resources):
"Self-confidence is a main factor in who moves to big cities. It’s self-confident young people, after all, who have the chutzpah to leave small towns behind. (An increase of the self-confidence percentile by one standard deviation raises the probability of initially moving to a big city by 12 percent, according to the study.) This decision compounds over time as younger workers in big cities gain the experience and background they need to get ahead in their careers and earn more money. Highly confident people with lesser abilities benefit the most here, since they gain access to the opportunities, networks, and experiences that these big cities provide."