Earlier quoted context omitted.
Hardworking and stupid make great employees though. The problem is for doing such a great job as cogs in the machine they get promoted into positions of authority and then it is hard to fault them too much because at least they are hardworking.
I think that here, lazy means "do as little as possible" and hardworking means "always do something", it doesn't mean people do or don't do as they are told. Lazy stupid is fine because these people will execute the order to the letter and then slack off. If the order is clear, there is not much damage they can do. Hardworking stupid will try to do more and mess things up. So if the order is to clean the toilets and…
So anyone not calling the plumber (or skilled at being one) who tries to clean it may end up in the dumps. An actual plumber will clean it after fixing or during fixing.