Exactly, the 80-20 rule also applies to unit tests. I don't have 100% coverage on big projects, but everything I write that's meant to go in production is in TD

Exactly, the 80-20 rule also applies to unit tests. I don't have 100% coverage on big projects, but everything I write that's meant to go in production is in TDD anyway, so there's always enough tests to prevent a junior from breaking my stuff, and I save a lot of time because thanks to TDD I don't need to manually test much, and most of the times not at all, I just wait for user feedback: it's always much easier to have code working in real conditions, if it already works in test conditions, not the other way around.