The invisible hand assumes that all demand will be met by supply. Price elasticity and profit margins can make it where all demand doesnt need to be met. For example healthcare... How are you supposed to make a walmart version of healthcare. And why would anyone want to do that? Its more profitable to set high prices (because regardless of the price people will NEED the service) and if someone can't afford it who cares... somebody else can. Even the few places that try to be reasonable still have to charge 15k for something like a gallbladder removal (and this place doesn't accept any insurance). That still requires most not to be able to afford it or have to go into fairly substantial debt for a health emergency that wasn't really their fault. I agree with Krugman about it being broad but not universal.