A language model demo is easy and a language model system is not. The gap between the two is almost never the model. It is the retrieval that returns the wrong three paragraphs, the prompt that was edited nine times with no record of which edit helped, the agent that had permission to do something it should never have been able to do, and the absence of any test that would have caught the regression before a user did.
Applied LLM work is therefore mostly ordinary engineering pointed at an unusual component. The model is non-deterministic, its failures are fluent and confident rather than loud, and it will happily produce a plausible answer from irrelevant context. Everything around it — how documents are chunked and retrieved, what the model is allowed to call, how its output is checked, how a change is measured — is what decides whether the system is trustworthy.
That is where the work goes: grounding the model in your data so answers can be traced to a source, giving agents a bounded set of tools rather than open-ended reach, and building an evaluation harness early enough that it shapes the system instead of auditing it after the fact.