No one is irreplaceable

Losing a resource is very different from losing a valuable resource. But however valuable someone is deemed to be, their tenure will one day end. Seen from a short term perspective, losing someone who is really good at what they do can cause some temporary inconvenience. Being good at what you do doesn't mean throwing your weight around or behaving as if the whole world revolves around you. Some people take competence as an excuse to throw the rule book out of the window and treat people badly. It's the same attitude that will render them replaceable one day

Life has gone on after the deaths and retirements of the most iconic people. Even if you are world's most competent person, the absolute best at what you do, you will one day be replaced. 'Let's see how you do it without me' or 'it's my way or the highway' won't win you plaudits. People don't always just remember the work, they also remember how you treated them.