it's funny- I kept fish for years without knowing ANY of this stuff and they did well. The water is soft here, but I couldn't have told you that a few years back. I've kept lots of fish the wrong way- usually what I would keep are considered hardy fish, so that helped, but I don't remember having much trouble keeping them alive- except I'd always have a few die when I started the tank if I didn't be patient and give it a few weeks with 2 or 3 fish max- I didn't know why, I just knew if I put too many in right away, they'd die LOL.
I still break the rules some, but do try to adjust a bit based on what I've learned. At the end of the day, though, I'll go with my experience. My personal opinion is that there are so many variables in water conditions, combined with somewhat rudimentary methods of testing, that provide almost as many exceptions as rules.
If I got into the hobby now and started reading before I dove in, I'd be terrified. Ignorance truly was bliss in my case.