In Short:
One marshmallow now, or an extra one in a few minutes if you can wait. Could your child cope? Could you?

In Full
“The marshmallow experiment is a famous test of this concept conducted by Walter Mischel at Stanford University and discussed by Daniel Goleman in his popular work. In the 1960s, a group of four-year olds were given a marshmallow and promised another, only if they could wait 20 minutes before eating the first one. Some children could wait and others could not. The researchers then followed the progress of each child into adolescence, and demonstrated that those with the ability to wait were better adjusted and more dependable (determined via surveys of their parents and teachers), and scored an average of 210 points higher on the Scholastic Aptitude Test.”

Source – YouTube/clap4thehandicap with thanks to The Presurfer for the spot