Those children who resisted eating the marshmallow (or cookie or pretzel or whatever) immediately in the 1960s/1970s became successful adults. They had higher rates of graduating from college, were healthier (in terms of lower BMI) and had higher incomes. Why?
If they are aggressive or sensitive, they may behave in ways that cause others to avoid them (rejected and neglected) and then, they don't have opportunities for age-appropriate socialization. Their social skills don't mature and the cycle continues.
There is help for kids with self-regulation and overall executive functioning deficits.
In the clinic setting, video games were used (cat in a rainstorm) whereby the child used a joystick to keep an umbrella over the cat. A researcher, Michael Posner, conducted sessions of 40 minutes each and found that children has "substantial increases in their executive function and executive control and even some increase in nonverbal IQ measures".
Kids need to appreciate and understand that there is a direct relationship between how they are behaving and "what happens to them" so they can chose their options. As parents, teaching them the "cause and effect" is critical to growth.
Dr. Mischel is working with economists from Harvard University involving some of the kids from the original studies who are in their "very late forties and early fifties" to explore the relationship between the two patterns of development of high and low self-control and economic outcomes. No news on when the results of the study will be completed, but if I find out, I'll let you know!