AI nails 80%, last 20% takes 5x longer

The fix

This is the universal vibe coding experience and it's not a skill issue. The first 80% is patterns the model has seen 10,000 times. The last 20% is your specific edge cases, error states, browser quirks, and integration glue — things no model has seen exactly. Plan for it. Block out 3x your gut estimate for the polish phase. If you keep promising "one more hour", you're estimating against the 80% phase.