The Stanford marshmallow experiment[1] refers to a series of studies on delayed gratification in the late 1960s and early 1970s led by psychologist Walter Mischel, then a professor at Stanford University. In these studies, a child was offered a choice between one small reward (sometimes a marshmallow, but often a cookie or a pretzel, etc.) provided immediately or two small rewards if he or she waited until the experimenter returned (after an absence of approximately 15 minutes). In follow-up studies, the researchers found that children who were able to wait longer for the preferred rewards tended to have better life outcomes, as measured by SAT scores,[2] educational attainment,[3] body mass index (BMI)[4] and other life measures.[5] However, recent work calls into question whether self-control, as opposed to strategic reasoning, determines children's behavior.
The purpose of the original study was to understand when the control of deferred gratification, the ability to wait to obtain something that one wants, develops in children. The original experiment took place at the Bing Nursery School located at Stanford University, using children age four to six as subjects. The children were led into a room, empty of distractions, where a treat of their choice (Oreo cookie, marshmallow, or pretzel stick) was placed on a table, by a chair.[1] The children could eat the marshmallow, the researchers said, but if they waited for fifteen minutes without giving in to the temptation, they would be rewarded with a second marshmallow.[1] Mischel observed as some would "cover their eyes with their hands or turn around so that they can't see the tray, others start kicking the desk, or tug on their pigtails, or stroke the marshmallow as if it were a tiny stuffed animal", while others would simply eat the marshmallow as soon as the researchers left.[1]
In over 600 children who took part in the experiment, a minority ate the marshmallow immediately. Of those who attempted to delay, one third deferred gratification long enough to get the second marshmallow.[1] Age was a major determinant of deferred gratification.

You see, back in the sixties researcher Walter Michael conducted the famous marshmallow experiment at Stanford University. He put 4 year old children in a room by themselves, placed a marshmallow in front of them and gave them a simple choice-
“You can have the marshmallow now or you can wait 15 minutes and get 2 marshmallows”
He then left the room and observed the child’s behaviour.
10 years later, Walter Michael surveyed the same students to see how they were going.
Interestingly, the children who had resisted eating the marshmallow had better school grades and social success than the children who ate the marshmallow straight away. They could also manage their stress levels more effectively and were less likely to have problems with their weight.

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So why were the students who had resisted eating the marshmallow better off?
Well, they were more likely to go to their classes, get on with doing their school work, resist eating unhealthy foods, etc. The simple reason being that they had better self control (willpower).
The good news is it doesn’t matter if you would have gobbled down the marshmallow straight away at the age of 4. Why?
Because self control is like a muscle: it can be strengthened with the right activities and lifestyle. It may feel uncomfortable or difficult initially, but the more you do it the easier it gets.