True! But not every highly-productive person is this. If you keep complexity low, you can have a "single point" without it being high risk.

Recently I was really proud of being able to take a half of a day to document all my systems to have a reasonable assurance that the documentation would contain all the info needed for someone else to step in if they need to and get something done.

And, it is a lot of systems! But we kept the complexity WAY down. And while the engineering is not perfect (is it ever?) I feel confident that someone can step in and work on these systems if I'm not here.