The Second Brain George's AI Works From

George B. Thomas calls it his main brain. It is a folder of plain files that holds what he knows, how he sounds and what his business has done, and his AI works from it. He has written the whole thing down in the Build Your Main Brain series. This page is the short version.

What it is

"On my computer, the folder is literally called main brain."

It started with four folders: Raw, Wiki, Intake and Journal. "I have more than four now, because I added areas for clients, websites and other things."

George builds it with Claude Code. "I use an app called Obsidian on top," and "I also push a copy to GitHub as a backup."

An early version lived on Microsoft's OneDrive, so it would follow him from computer to computer. His summary: "It didn't go well."

Read the full story: What Is a Second Brain?

What went wrong first

Early on, the system quoted George saying things he never said.

"I had never said any of the things that it was actually quoting at all."

The cause was the source, not the model: "I gave it the folder that was the summaries of the meetings and not the actual real transcripts."

The brain also keeps itself tidy: there is "a cleanup command I run called dream," and "the journal like self-writes itself."

Read the full story: Intake, Raw, Wiki

How it knows who is talking

The brain holds identities: files that tell the AI who is speaking and how.

• A rule before it writes: "My system won't write in a new voice until it has at least three real samples."
• Company and person are linked: "my company identity file has a parent and that parent is my personal identity."
• Where the voice came from: George worked through his podcast with his AI, one episode at a time. "I did that for 60 episodes." Then he asked it to name the top 25 mindsets, core values and beliefs across all of them. "That became the foundation my assistant writes from."

Read the full story: Why Identities Matter

A story bank it can reach into

"My bank has more than 2,100 cards in it."

"One story is one markdown file." The AI does not load all of them. It reads "a menu file, which for me is under 80 lines," and pulls the cards it needs.

Read the full story: Your Story Bank

Keeping AI from putting words in his mouth

George keeps a record of the times his writing agent produced something it should not have. "So I built a positions list": what he claims, what he rejects and what he has not ruled on yet.

He is plain about the limit. On one draft, "my AI editor still found four problems, all the same one." And: "My writer is decent at reporting its own uncertainties, but it's a poor police officer."

Read the full story: Repeat, Don't Invent

It goes where he goes

"My brain has three versions online."

Because the brain is files in a repo, "I can open the same repo on my laptop, or any computer, and pick up where I left off."

Read the full story: Make Your Second Brain Portable

How he works in it

"I spend 70 to 80% of my time in plan mode."

And the human stays in it: "The last 10% is still mine."

What is still open

• "It's still growing."
• George notes that "the AI plan I use for my own builds is a consumer plan," and a consumer plan doesn't come with a data processing agreement. That matters for client material. Read: How to Add Clients to Your Second Brain.

The series

Start with Human-Powered, AI-Assisted, then What Is a Second Brain? The rest of the series follows from there.