What does it mean that one idea per container?

A note that captures exactly one idea can be understood without its original context, linked to any argument, and recombined indefinitely — a note that captures two ideas can do none of these things reliably.

Example: You finish a meeting where the CTO proposed migrating to Kubernetes and also mentioned the team needs a better on-call rotation. You write one note: 'CTO wants K8s migration + better on-call.' Three months later, you're building a case for on-call improvements and search your notes. This note surfaces, but it's tangled with the K8s migration context. You can't link it to your on-call argument without dragging in irrelevant infrastructure decisions. Two separate notes — 'Migrate orchestration to Kubernetes: CTO rationale' and 'On-call rotation is burning out the platform team' — would each slot cleanly into the arguments where they belong.

Try this: Open your note system and find your five most recent notes. For each one, ask: does this note contain exactly one idea I could explain in a single sentence? If a note contains two or more distinct ideas, split it. Create one note per idea, give each a clear title that states the claim, and link them back to each other. You should end with more notes than you started with — and each one should be a standalone unit you could drop into any future argument.