Most of the popular language about the nervous system frames it as fundamentally defensive. Capacity, in that framing, is something you build by overriding your body's protective default. This is partial, and somewhat backward.
The nervous system is, more accurately, a dynamic system for managing energy, prediction, and engagement with the world. When the system has the resources to operate in its full range, it offers connection, exploration, flexibility, and complex emotional experience. When the system is under constraint, it narrows toward stability, which often feels like protection.
What gets called a protective nervous system is usually a system operating near the edge of its current capacity, where uncertainty and variability have become costly.
This distinction matters more than it sounds like it should. If the nervous system is fundamentally protective, the work of building capacity is the work of overriding defense. That framing puts the practice in opposition to the body. If the nervous system is fundamentally dynamic and narrows under constraint, capacity is what becomes available again as the constraints ease. That framing puts the practice in partnership with the body.
XRegulation is built on the second framing. The work is not about getting calmer. It is about restoring the conditions under which the nervous system can engage its full range. That range is what we mean by capacity.