I watched a GPT-4 function call that worked perfectly in the playground silently fail in production. The output was valid JSON. The structure was correct. But the content was a hallucination. It took me two hours to notice the problem, and another day to build a guardrail that caught it.
That moment taught me something I now tell every founder I work with. The first 20% of an AI feature takes 20% of the time. The last 20% takes 80%. Not because the code is hard. Because the code is the easy part. The hard part is everything around it.
I've built production AI pipelines at scale. A job board platform that scores 10,000+ listings daily with LLM function calling. An AI resume tailor that generates dozens of tailored resumes in a single session. A meeting assistant with real-time transcription. Every single project followed the same pattern. The demo worked in an hour. The production system took weeks.
Here's what that last 80% actually costs.
The Prompt That Broke on Real Data
