People should start using these apps as simple note-taking apps and extend/adapt them based on their needs, rather than diving head-first into these complicated methods/systems to form a "second brain".
If you go straight into OPs system you'll spend way more time trying to figure out how it works (and it might not even work for you) rather than getting actual work done
Start simple. Write a few notes. Maybe you need to draw things: add Excalidraw. Maybe some note structures are similar: consider Templater.
> People should start using these apps as simple note-taking apps and extend/adapt them based on their needs
This. I'm a hardcore Obsidian user both at work and at home, and I started both vaults from absolutely nothing - no user scripts, no organisation, literally no plan at all. Since then, they've evolved and optimized in radically different ways. Taking someone else's "system" is just a way to fool yourself into thinking you can be more productive than you are; you have to find that for yourself and what works specifically for you.
My personal vault is geared much more toward organizing creativity, with a little bit of task-oriented stuff and technical documentation, while my corporate vault is heavily schedule based and contains mostly tactical information, meeting notes and thoughts, etc. For it to be a "second brain", you need it to model your brain - and I work very modally. I have a "work mode" and a "non-work mode" that order things pretty differently, and it shows in the hierarchies and organization of both vaults.
Interesting that you have so few vaults. I have dozens of them, each for a different project, or for different aspects of the same project. The way folders work in Obsidian is quite bad, when I am creating a new note it insists in putting it into the top folder instead of in the folder where I am currently in, so I prefer to keep it flat. I am just using the default setup and cannot be bothered much with plugins. There is no proper API documentation either.
Exactly. At its core Obsidian and similar apps allow you to make notes, connect them easily _and search for them_ using GUI. That's it. That is how I try to explain what it does to someone interested. These modern apps are a huge step forward, if someone prefers emacs or vim/fzf - no problem.
If you go straight into OPs system you'll spend way more time trying to figure out how it works (and it might not even work for you) rather than getting actual work done
Start simple. Write a few notes. Maybe you need to draw things: add Excalidraw. Maybe some note structures are similar: consider Templater.