Ok so, "ignoring reality" wasn't a good way to frame this. I see and understand your point. I'm not sure assuming we don't change (or much) is a good way to frame this either, even though past precedence could more easily be used to make a model.
BTW how do you plan/model for an outcome without historical precedence?
Theoretically it'd be purely rational, but realistically our entire understanding of the social is so historical I doubt that's possible.