The Sacral Center
The engine. Whether you have one decides your type before anything else does.
Defined Sacral
You have a self-renewing energy source and a gut that answers before your mind does. This is what makes someone a Generator or a Manifesting Generator, and the energy renews properly only when it has been spent on work you actually responded to.
Open or undefined Sacral
You have no consistent engine, which means you are not built to work the way most of the world is organised. An open Sacral borrows energy from whoever is nearby, feels it as their own, and burns past its limit without noticing.
The not-self theme: Not knowing when enough is enough. Working like a Generator when you are not one, and calling the resulting exhaustion a character flaw.
What an open Sacral eventually becomes
An open Sacral learns exactly how much energy a room holds, and gets very good at leaving before it is spent.
This is the part most people miss. An open centre is not a deficiency to be fixed. It is where you take in and amplify other people, which is uncomfortable for years and then becomes the thing you understand better than anyone with it defined.
The gates of the Sacral
9 of the 64 gates sit in this centre. Each is also a Gene Key, read as a Shadow, a Gift and a Siddhi rather than as a mechanic.
Centres, gates and channels come from the same tables the bodygraph is drawn from. Human Design was assembled in 1987; Six Mirrors reads it beside five older systems and shows where they agree.