It was also highlighted (recently?) iirc that it has little to do with discipline and will-power, but is surprisingly affected whether kids come from wealthy / "good" families (and thus can trust grown ups) vs kids coming from poorer / "troubled" families (and thus just leap at the opportunity and don't trust that they will actually get another marshmallow if they will wait).
It was also highlighted (recently?) iirc that it has little to do with discipline and will-power, but is surprisingly affected whether kids come from wealthy / "good" families (and thus can trust grown ups) vs kids coming from poorer / "troubled" families (and thus just leap at the opportunity and don't trust that they will actually get another marshmallow if they will wait).