Suppose a customer-support assistant receives the following question:

What does error code ZX-4821 mean?

The answer exists in the knowledge base. One document contains the exact code, followed by a short explanation of the hardware failure that produced it.

Yet the retriever does not return that document.

Instead, it retrieves three passages about common device errors, troubleshooting procedures, and hardware diagnostics. Semantically, the results make sense. They discuss the correct product, the correct type of problem, and the correct general topic. But none of them contains ZX-4821 .

The embedding model understood everything except the one string that mattered.

Now consider a second question:

Can I get my money back if the product arrived broken?

The relevant policy never uses the words "money back" or "broken". It says that "customers are eligible for a refund when an item is delivered in a defective condition". A lexical search may miss it entirely.…