Not surprisingly, some of these differences were correlated with intelligence and social class and race—but all these results remained significant even when those factors were taken into account. In a follow-up study, the same researchers looked at brothers and sisters from the same families so that they could compare children who grew up in similar homes. Again, over and over, the sibling with the lower self-control during childhood fared worse during adulthood. They ended up sicker, poorer, and were more likely to spend time in prison.
