Ask HN: How tolerable is infrastructure to skilled worker availability?

Looking at reports this morning about delivery drivers showing up to work sick, I started to wonder how much tolerance various parts of our infrastructure have to fluctuations in the worker pool.

If we constrain the question to only consider the maintenance aspect of power plants, water systems, undersea cables, satellite control, etc... what level of tolerance is there to worker shortages? It seems unlikely that any one of these would have any sort of equivalent to a operational manual that a layman could use.