The 80% Problem: The Last 20% Is Where the Engineer Used to Live

# Summary AI tools can rapidly generate the first 80% of working code—the basic logic and demo-ready scaffolding—but consistently skip the final 20% that requires deep engineering experience: handling edge cases, concurrency issues, production failures, and operational resilience like rate limiting and circuit breakers. This final 20% has historically been where engineers developed critical judgment through hands-on debugging and system failures, but AI's speed creates a risk of shipping incomplete systems that fail under real-world conditions.