Self-control more difficult for social outsiders.

A recent study in this month's Journal of Personality and Social Psychology (Vol. 88, No. 4) suggests that social exclusion reduces people's ability to self-regulate or defer gratification. The conclusions are interesting in their suggestion of a tight link between ability to self-regulate and rationality:

These findings make sense, the researchers say, because regulating our behavior is what allows us to fit into society and be accepted in the first place. People who are rejected may feel that their self-regulation efforts were for naught and be less likely to self-regulate in the future. In fact, a follow-up experiment in the study suggests that rejected people are merely unwilling, not unable, to self-regulate.