'Stop acting like you're important!': Performance collapses when boss tells worker to do their own job instead of the extra work they had been doing

Being told to just do your job is kind of fair; it is your job, after all, and the reality of the world is that at some point, it's going to be necessary for you to step in line and let someone else call the shots. Still, is it really fair to say, "Just, do your job," when it's not really your job in the first place? Rather just that someone else has decided that your job is to do their job too? There's a reason why your boss is paid more to go along with the responsibility that has been handed to them, and handing that responsibility off to your lowest-paid team members isn't really what anyone had in mind when they put you in that role. 

Regardless, if you were just told to "Just do your job" by someone who wasn't doing theirs, you might not take that so well. And when they appointed someone else to do the job you supposedly weren't doing, only to have things come crashing down, you might take some solace in that.