Earlier quoted context omitted.
As a former submariner (but not an astronaut, tbf), I think they’re on-par. They both actively want to kill you at all times.
In total failure mode, yes. But with one of the two though there are other humans not far away to send help, and land/open sea to rise up if you see a problem emerging. In space it can be nightmare to get any help or get back if something goes wrong.
It was a strange and isolating feeling the first time something broke underway, and I realized there wasn’t someone to ask how to fix it. It’s also a great builder of grit and determination, or of hopelessness. People tend to go one way or the other.
Being awakened with a flooding alarm when drills were not scheduled, for example – I realized afterwards (as did everyone else, I assume) that if faced with an actual emergency, I could keep my cool and work the problem. [0] It’s a good feeling, especially when you know you can trust the other 100+ people around you to do the same. Incidentally, it was not technically flooding (unplanned water ingestion at a rate greater than the capacity of dewatering systems), but sure as hell looked scary when they demonstrated the flow rate seen later.
[0]: I personally think this is why Navy Nukes (especially submariners) make great SREs. The fact that a Nuke helped build Google’s SRE program probably helps.