There's another problem not really addressed here; when the requirements you get from the customer are wrong/make no sense/could be done better another way/are

There's another problem not really addressed here; when the requirements you get from the customer are wrong/make no sense/could be done better another way/are for things they won't actually use/are a part of some internal political struggle. This is something that crops up quite frequently in my work. We'll get a requirement like this: "the app should use HTTP like a web browser, not a different protocol". On inquiry as to why it's so important for something that's not a web browser to so strongly resemble a browser, the answer will be something like, "so we don't have to ask IT to open a firewall port". The person deploying the software could just fill out the paperwork, but they find it easier to "require" that the software sneak past their own corporate security controls. This is the sort of requirement that is real in some sense and not in another sense, depending on whether you define the customer as whoever you're talking to on the phone right now or the business as a whole.