In the classic experiment of Walter Mischel, a marshmallow is placed in front of kids with the following instruction: "You can eat it now or wait but if you wait, I'll give you another one." Longitudinal research has followed the kids and concluded that the ones who were able to delay gratification became more successful in life and were able to follow their goals more consistently.
Here is a cute video about a modern version of the experiment:
Well, since the original experiment results were published, quite a few researchers tried to repeat it and they could not always support Mischel's original findings. They have said that it is affluence and not willpower that seems to be behind some kids' capacity to delay gratification. Also, they found that poorer kids had more trouble with waiting.
Despite the professional debates around it I love this experiment. I think it reveals the development of a very important human characteristic: self-control. We cannot have everything at the very time we think of them, for the most important events and belongings in our life we need to wait patiently. And it is not bad if we start to learn it in childhood. Perseverance and consistency also stem from this ability. So let's train our self-control!