The blind spot problem
I had Claude add input validation to an API endpoint. It wrote clean, idiomatic TypeScript. I asked it to review the diff. It approved it. Tests passed. I shipped it.
Two days later a colleague pointed out that the validation silently accepted empty strings — which the original spec explicitly prohibited. Claude had written the validator, approved it, and neither caught the gap.
When I went back and asked Claude why it missed it, the answer was essentially: "I interpreted the requirement as non-null rather than non-empty, which is a reasonable reading."
That's exactly the problem. A model that wrote subtly wrong code doesn't just fail to catch the bug — it actively defends its interpretation. It doesn't have independent judgment about its own output. It has motivated reasoning.
