Worse, the method has numerous private dependencies on code that makes database or service calls. Or just dependencies that have nothing to do with what I'm testing. Just today I tried to instantiate a class, but failed because of a class two inheritance levels up with a dependency on another object being properly instantiated and configured. Figuring out how to test that is going to be a nightmare that eats up a lot of time.
If I was allowed to only do TAD and not TDD, I'd scrap it and invest more in end-to-end testing.