The words of caution are good, don't get me wrong. Man when I think back at some of the stuff I did it would be really scary, still can get in over my head in a hurry especially when doing semi routine stuff. Biggest threat in numbers is doing the job, dropping something on your foot, eye injury or falling off a ladder.
I worked on thousands of equipment over the years, right from the start, most of it worked, even back in the day I never have a catostrophic failure and no real extreme failures despite my ignorance, seen it broke where it had to be removed from service, repaired a lot of stuff over the years and left it in far superior condition than it was. Seen a lot of work done by people with the "legal right" to be doin it that had absolutely not a clue, they should been school teachers or sumpthin else.
Even most sloppy work doesn't fail and lots of engineered stuff does. The paper work just makes it easier to sue someone. I was on a nuke, you be surprised how much needs to be re-done because first guy that did it just didn't know how. There a lot of plumbers playing fitter.
The threat of extreme catastrophic tends to be highly over rated.