@futurebird As it turned out, the marshmallow test research wasn't reproducible. They tried a few times over the last decade or two (here's one article: https://www.vox.com/science-and-health/2018/6/6/17413000/marshmallow-test-replication-mischel-psychology)
It did prove, however, that some people are just all too eager to seize upon findings that reinforce their preexisting beliefs and become "conservatives" who refuse to change in the face of contrary evidence.