Back in 1972 there was a famous psychological experiment carried out known as the Stanford Marshmallow Experiment.
The study has received a lot of recognition over the years, being replicated many times and even being criticised quite heavily at times.
The basic principle was to offer children aged 4 the choice between receiving a reward immediately (marshmallow/pretzel/sweet) or two rewards if they were able to wait 15 minutes. This proposition is a test of the ability for a person to delay gratification in the present, for a larger reward in the future, effectively testing their self-control. The findings showed that children, as expected, were often quite bad at controlling their impulses in the short-term to obtain a greater prize in the longer term. Effectively, it proved that our logical, long-term, human brains are not as well developed at that age, and our impulsive chimp brains are far more likely to dictate our actions.
Discipline is choosing between what you want now and what you want most
Augusta F. Kantra