Mischel was testing the capacity to delay gratification. Delayed gratification refers to the ability to resist the initial temptation to take a reward immediately, and rather wait a bit to get an even better reward later. So, he wanted to see if children would eat one marshmallow immediately or wait a bit for him to return so that they can eat two marshmallows instead of just one.
The North Korean economy is based largely around self-sustainability. Everything is owned by the government, everything is planned by the government. How much, in which way, in what will be produced and consumed is planned by the government. This results in a very fragile economy above which always lurks the possibility of crack down. The slightest mistakes in the planning, or if some natural disaster occurs, always leads to huge economic problems. It is very common that the people are suffering from malnutrition because the planning didn't turned out as predicted. The economy has growth one year, stagnates another, drops in the next, and it is all very unpredictable.