Well, there are the people who don't want to learn and improve their bad practices. They're awful. I worked with someone like that-- the only time I actually asked someone to fire someone. He was brilliant and had a lot of experience, but he had some awful practices that he refused to improve, and that made everyone else less productive. He manage to position himself as the "star" kicking out 4000 LoC per week, until it became clear that not only did none of his stuff work, but it was illegible and couldn't be made to work.

That experience tested me. But if you have someone who's very junior, he's going to make the same kinds of infuriating mistakes, but not out of malevolence or a negative attitude-- just being new to the whole process. We were all there once.