My favorite was going through the Nix reference manual. Section 4.2, Profiles
> If the profile doesn’t exist, it will be created automatically.
Nope! If it doesn't exist then running the commands this tells you to will bork your installation completely, and unrecoverably with the knowledge you have gained up until that point in the book, at least without starting from scratch again.
Search for issue - closed in 2018, wontfix as "It's documented correctly and quite clearly." by someone who apparently didn't read or understand that the literal reference manual tells people to break their installation.
I have never touched Nix/NixOS since, because clearly they don't want or need people without 100% of their lives to dedicate themselves to it.