Why do you say the assistant is the interface and the brain is the product?

Because the assistant is only how people talk to the system. The real value is the controlled knowledge it can draw from. If the business brain is weak, the assistant has nothing useful to say.

When the brain is strong, the assistant becomes a practical interface for customers, staff, managers and AI-readable public outputs. That is the difference between a toy chat window and a business asset. A Digital Twin is broader than a chatbot because it includes approved business facts, public Q&A, image context and machine-readable outputs, not just a chat box. In other words, the goal is to give the client a controlled first AI layer instead of leaving the whole topic vague and undefined.