There is no such presumption. I can assure you supply and demand works the same way, even when behaving randomly. Perhaps you mean that people don't behave in

There is no such presumption. I can assure you supply and demand works the same way, even when behaving randomly. Perhaps you mean that people don't behave in a way you deem "rational" and that therefore the outcomes are different from what you expect. That is an issue with your model of reality not being accurate, not with the concept of supply and demand.