A support agent that answers 'our return window is 45 days' when the actual policy document says 30 is not making an isolated mistake — it is demonstrating that nothing in the pipeline checked the answer against the document it was supposedly built from. Retrieval-augmented generation is often described as a hallucination fix, but retrieval alone only changes what the model reads before it answers; it does nothing to guarantee the model's answer actually reflects what it read. A model handed the correct 30-day policy text can still write 45 days, because generation is a separate, unconstrained step downstream of retrieval, and nothing forces the two to agree unless something is built to check.
Grounding is that check: a mechanism, external to the model's own confidence, that verifies a generated claim is actually supported by the source material it claims to draw from. Citation enforcement is grounding's most visible form — requiring the agent to name which passage of which document backs a claim, and then validating that the cited passage exists and actually says what the agent claims it says, rather than trusting the citation string on its face. A citation the model invented is worse than no citation at all, because it looks like evidence while carrying none.
What breaks without enforced grounding is the entire premise of using retrieval to make an agent trustworthy. A retrieval pipeline that fetches the right document but lets the model paraphrase freely, with no check that the paraphrase preserves the source's meaning, gives users the appearance of a well-sourced system while providing none of its actual guarantees. The gap between 'we retrieved the right document' and 'we verified the answer matches it' is exactly where grounding failures live, and it is invisible until an audit — or a user — catches the mismatch.