And interestingly, those who volunteer for the military who are of all races and sexes often seem to do quite well after accepting the discipline that is taught there. 

Of course, the military has both positive and negative feedback for those who participate.   In eight to 12 weeks most of them respond and meet the standards required for all.  But it is a self-selected group; it is composed of those who want to improve and are willing to work and acknowledge discipline to do so.