This all sounds good — only it’s wrong.
The Marshmallow Experiment exists, but it demonstrates something quite different to what you have written about. What’s more, what it demonstrates is both more interesting and more useful. Sadly journalists have misunderstood this study since the day it was publicised and reported it the way you have. It’s a shame that this keeps happening.
As Hannah suggests below, I recommend listening to Invisibilia’s podcast about it.