In social psychology, there is a small industry for articles reporting positive correlations between measures of self-control and various measures of socio-economic status and achievement. For example, Tangney, Baumeister and Boone (2008) found that self-control, measured on a self-report scale they devised, is correlated with better grades, somatic and mental health, and stable social relationships such as marriage. Moffitt et al. (2011) conducted a longitudinal study that followed children who had participated in the Mischel “marshmallow tests” to the age of 32 years old, and found childhood performance in that delayed gratification assignment to be correlated with measures of health and economic success, interpersonal adjustment, and with criminal justice outcomes, even after controlling for childhood socio-economic factors.
Studies like these have been widely publicised, and the message in popular science media often leads with the idea that self-control is a stable trait that some have, some don’t. The ones who were dealt a losing hand in self-control got a losing hand overall, ending up with poor health, poverty, unstable relationships, and crime not out of ill will, but because they simply can’t hold it together. In short, the causal arrow goes from poor self-control to socioeconomic disadvantage.
This line of thinking has received plenty of criticism. Some have pointed out that the studies have been designed from a perspective assuming a middle-class lifestyle, and that self-control may not be as adaptive for people from all backgrounds.