Everyone is talking about a second brain. Almost nobody says what it is actually for It is not a note app. It is what stops you researching the same thing twice. The part nobody stores, and you can start today: keep a rejected file. Every claim you checked and threw out, with the reason. A vendor number that appeared nowhere outside their own blog. A stat that turned out to be from an older release. A repo that looked good until you read the licence. It works the same outside research. Candidates you passed on and why. Tools your team trialled and dropped. Features you decided not to build. Suppliers you quoted and rejected. Everyone saves what they found. Almost nobody saves what they ruled out, so six months later somebody rules it out again from scratch. That reasoning lives in one person's head and nowhere else. I keep mine in HippocampOS. Facts with the source attached, and a separate brain per role so nothing bleeds between them. Asked one brain about a topic I never gave it, and it came back empty rather than inventing something. Graph below is a 15 minutes of loading. Add HippocampOS to your work at: