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

1. Check the problem

The first 80% is patterns the model has seen before; the last 20% is edge cases and integration glue it hasn't. Block out 3x your gut estimate for polish. Promising "one more hour" means you're still underestimating.

2. Use the prompt

We're at the last 20% of [feature]. List every remaining edge case, error state, empty state, loading state, and integration seam that production needs but a happy-path demo skips. For each, say what breaks if it's missing and give the fix. Be exhaustive and assume nothing is handled yet.

3. Verify the fix

Review the proposed diff, run the relevant checks and exercise the original failing flow before merging.