The usual explanation for a bad requirements document is that it was written badly: vague language, missing edge cases, no sign-off process. Those problems are real, but they’re rarely the root cause.

The failure usually happens earlier, at the point where the writer decides how to group the requirements. Group them by feature and you get a document that reads well but hides dependencies. Group them by team or department and you bake organizational politics into the system architecture without meaning to. Group them by the actual functional domains the product needs, shared data, distinct workflows, integration points, and the document starts telling engineering something true about how the system needs to be built.

That grouping decision happens before a single sentence gets written, and it’s the part that’s hardest to redo once a document is underway. Worth getting right before the writing starts, not after a first draft gets pushback.