I design and conduct space missions, and I'm an experienced professional pilot. The answer to your question is "never."

Any system that requires perfect performance from any one human will fail.

There are millions of people who are self employed in an industry where they could be maimed or killed if they screw up who manage to make it to retirement.

I think the better question is how you get a system in which people are only responsible for any one facet to get the same performance out of people that a painter can get out of himself when he's setting up his own ladder that he personally has to climb on.