Nothing. I don't have any confidence in my ability to write error-free tests.

If I had started with test-first approach, I would have saved half a day or so.

TDD helps me avoid mental rabit trails of nice-to-haves and performance improvements.

When I work on a project that relies on manual verification, I'm never confident. I never feel sure of the work I'm doing.

...which is often actually an asset.

Painting without a drop cloth may be faster, but the hours of clean up outweigh savings.

Maybe strict TDD isn't necessary for experts, but it's still useful to learn.

It's not the red/green/refactor cycle. The important thing is working in short test/code or code/test cycles.

An airbag broke my arm. BDUF would have saved time. Test-first wasted effort. Should abandon these?

Test-Driven doesn't only apply to normal code.

One of these skills, if you're good at it, diminishes the need for the other other.