How to build a second brain as a software developer

I've tried to incorporate some of the ideas of the "second brain" and it didn't really give me that much. My lessons:

1. It's always super helpful to write things down. Taking notes from what I read/learn is a great way to verify that I understand it. It sharpens my thinking.

2. However, maintaining the "second brain" is a lot work. It's not only about "linking" together notes. You also need to maintain some consistency between them. I ended up spending a lot of time thinking about the structure instead of actually thinking about the content.

3. Most of my notes/thoughts fall into two categories: (1) Either they are critical for something I'm actively working on or (2) it's just loose concepts that I'm toying with. For (1) I immediately end up playing with it in code — which is far more concrete and tangible than notes. And for (2) it was rarely important to retain the knowledge accurately many weeks/months later.

What I've ended up with is taking a lot of notes, but I hardly focus on organizing them.

Writing as someone who uses mind maps as part of my kit, I empathize with your comment. For my purposes, I've found that it helps to focus the map around a specific objective, project, etc. If I'm preparing a paper or presentation, it's helpful to see how the content can be structured, what can be pruned and what relationships between concepts there are. For project work or other objectives, I find them to be helpful in tracking and guiding learning.

FWIW, I use iThoughts across a couple of different devices. It's been around for a while now and has a good mix of usability and functionality.

My second brain is the 400 browser tabs that I have open

You might have meant this as a joke, but I honestly think this is a better way of doing things than a rigourously designed system of organisation and workflows and all that.

There are a million ways to approach this kind of thing, and whilst browser tabs aren't nessecarily the best way, they're certainly up there

You should definitely check out BrainTool (https://braintool.org)