The capacity framework starts from a different premise. The nervous system is not primarily a defective version of a normal system. It is a dynamic system that operates across a range, and the range narrows when the system is under constraint.
The same person, in conditions of adequate resource, can engage difficulty, recover from stress, regulate emotion, sustain attention, and remain present in challenging moments. The same person, in conditions of insufficient resource, cannot do those things.
What gets called anxiety, in this framing, is a nervous system operating in sustained sympathetic activation because the conditions it is reading no longer permit a return to baseline.
What gets called depression is a nervous system operating in low arousal because the system has determined, accurately or inaccurately, that engagement is no longer worth the metabolic cost.
What gets called emotional reactivity is a nervous system whose range has narrowed enough that small triggers produce large state shifts because the buffer between baseline and overwhelm has eroded.
In the capacity framework, each one is a system communicating about its conditions. The work is to restore the conditions under which the system can engage its full range again.