[rekrsiv]

Can a single human being reliably and robustly maintain a safety-critical system alone under any circumstances, ever?

Ever?

[_moof]

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.

[cucumber3732842]

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.

[pythonaut_16]

I don't think the GPs point is about personal safety of workers, but rather critical safety systems that rely on one person with no backups. Like an ATC tower for a busy airport staffed by a single person on an overnight shift.

A painter who does a bad job setting up a ladder is going to have a bad time, a lone ATC operator having a heart attack potentially puts multiple large aircraft full of people in danger...

[bombcar]

The goal should always be to reduce the human dependency - where reasonable which is where all the argument is, because of the cost/benefit analysis.

Mandatory scaffolding for roofing contractors would save some amount of deaths/injuries (and the related expenses) but add expenses to each job.

Some roofing firms refuse to operate without scaffolding; you pay for it or you find someone else.