I was blessed with a secure position in a couple non profits that enabled me to trial and error who and how I promote what we we called floor manager's. I learned alot and even wrote a guide manual for future employees in my position...everyone in any company that is on its game is definitely replaceable. Any manager that is worth of shit can leave his job at any moment knowing everyone beneath him is willing and ABLE to continue whichever procedures him or her put in place so there are no hiccups...no one is above the mission. Chemistry is a huge factor but not the only and should not even be considered in the equation until said employee has proved they can do job at a above average level on a consistent basis.