The hardest part of a complex agent build is often the architecture. So when LangChain publishes posts on their 'paid media agent' or a generic agent 'harness', it's tempting to treat them as a blueprint. The gotcha is that these are high-level concepts, not implementations. The articles don't include code, performance metrics, or the actual challenges they hit. They show you the big boxes in the diagram but skip the hard parts: the exact tool schemas the API retry logic, the specific validation layer that keeps the agent from breaking on an edge case You end up with a map that's missing all the roads. If you've built a custom agent harness, what's one piece of the glue code validation, state management retries that the public case studies always seem to skip?