The assumption every RAG demo makes

Standard RAG assumes the user's question maps onto one vector search. One query in, one embedding, one top-k lookup, one answer.

That assumption holds up in demos, because demos ask demo questions. "What's our parental leave policy?" is one document. Retrieve it, stuff it into the prompt, done.

Then you ship, and a real user types: "Did the carrier rate change we approved in Q2 actually reduce our cost per shipment in the Northeast, and does that hold if I exclude the Boston depot?"

That question needs a policy document, a rate table, a transactional aggregate, and a filtered re-computation. Your retriever will embed the whole sentence, find the three chunks nearest to it in vector space, and hand the model text that is topically adjacent and factually useless. The model, being a good sport, will answer anyway.