I remember in the distant past a video about a 'study' of kids who are given a marshmallow, and they are left alone with it after being told that if they don't eat it, they can have more later - but if they eat it now, that's all they get.
And later I heard that they looked into the kids that had 'poor impulse control' because they ate the one marshmallow ... and these kids apparently had grown up in an environment where promises were often broken.