BTW as a pitching or hitting coach you are always a bit on the mercy of luck too.
There are definitely good and bad coaches but there are cases where a PC is going to be scapegoated even if he did a good job.
1 or 2 injuries and a couple guys slumping and even a well respected coach can fall out of favor quickly.
It is a tough job and so much can go wrong in pitching, one guy from baseball prospectus famously said there is no such thing as a pitching prospect, meaning everyone can get hurt or be bad suddenly.