Chapter 10. Obsidian — a second brain that stays on your machine

Key points

• Obsidian is a free tool for managing and editing Markdown
• Its defining feature is that everything is stored on your own computer
• For a therapist, it is a knowledge base where safety and usefulness meet

What Obsidian is

Obsidian is a free tool for managing and editing Markdown files. Its defining feature is that it

stores every file on your own computer

For a therapist, this is decisive. Recall Principle 3 from Chapter 2: the safest thing is to keep it local.

Never uploaded means never leaves.

Obsidian is a knowledge base that delivers exactly that. Even notes containing patient information can be managed safely inside your own machine. When you want to consult an AI, copy across an anonymised portion only. That split is what makes safety and usefulness hold together.

How it differs from Gemini Notebook and cloud notes

• Gemini Notebook and cloud note apps → information is stored on someone else's server
• Obsidian → information is stored only on your computer (cloud sync is optional and can be left off)

Which makes Obsidian the right place for

• clinical notes containing patient information
• unpublished research ideas
• a record of your own thinking

— anything you would rather not send out.

Growing knowledge in Obsidian

Obsidian's strength is not only storage but connecting notes to one another.

• Links: connect one note to another with [[ ]]. Jump from a note on the shoulder to a note on rotator cuff tears in one click.
• Tags: classify with #assessment, #literature-notes and search across them later.
• Growth: write up what you studied, what you read, what you noticed in the clinic, a little at a time.

Notes that start scattered become, as links accumulate, points joining into lines, and eventually a map of knowledge that is yours alone.

This is exactly what the world of intellectual production calls externalised thinking. Rather than processing everything in your head, you put it outside, connect it, and grow it. AI becomes the partner that organises and extends that map with you.

Start as a plain notebook

Trying to use links and tags perfectly from the start is a route to giving up. At first:

• install Obsidian
• create one Vault (the folder where notes live)
• write what you learn, one theme per note

Using it as a plain notebook is enough. Once you are comfortable, connect related notes with [[ ]]. That alone starts to make knowledge three-dimensional.

Try this

Install Obsidian (obsidian.md) and create a vault. Move the 20260529_markdown-practice.md from Chapter 9 into it. Your second brain starts growing here.

Chapter 10 summary

• Obsidian is a free tool for managing and editing Markdown
• Everything stays local, which suits information you do not want to send out
• Start as a plain notebook, and connect with links once you are comfortable