> But how do you unambiguously specify "what is needed"? You don't. You follow the scientific method of building a model specification for "what is needed", th

> But how do you unambiguously specify "what is needed"? You don't. You follow the scientific method of building a model specification for "what is needed", throwing it into the world, and tweaking and improving it where you find that some of its properties are not a good fit for the problem it's intended to solve - primarily by gathering feedback from the people that are using it and finding its flaws.