This is very true. I recently left a position as a developer where I may have been considered irreplaceable by some. I had worked with some systems and website

This is very true. I recently left a position as a developer where I may have been considered irreplaceable by some. I had worked with some systems and websites for so long I became a fixture of this organization. When opportunities and change were presented to me from higher-ups in my organization my direct supervisors took it upon themselves to do everything in their power to prevent it. It wasn't pretty, there was plenty of drama, guilt, and even some underhandedness. Needless to say I found a new position ASAP. In my new position I'm replaceable. I believe that if I left today someone could take my place relatively easily. However, I'm much happier and it's refreshing to feel like I have mobility in my career again.