Ageing may begin locally. Decline becomes dangerous when it stops being local.
One biological domain can deteriorate while the rest of the organism remains relatively resilient.
But domains do not operate independently.
The body is coupled.

• Inflammation affects vascular function.

• Endocrine disruption affects metabolism.

• Poor sleep alters hormonal and neurological regulation.

• Digestive dysfunction influences nutrient availability.

• Environmental burden can increase detoxification demand.

• Reduced movement affects muscle, insulin signalling, circulation and endocrine communication.

The important transition occurs when several deteriorating processes begin reinforcing one another.
16×1 describes this as:
DEGENERATIVE VECTOR CONVERGENCE
Multiple negative directions begin converging.
At first the body compensates.
Then reserve diminishes.
Eventually the network may cross a:
CASCADE THRESHOLD
At that point, what began as several individual weaknesses begins behaving as one interconnected decline.
The inverse can also occur.
Improve several high-leverage domains simultaneously and positive effects can begin reinforcing each other.
That is:
REGENERATIVE VECTOR CONVERGENCE
This is one reason 16×1 focuses not simply on disease labels, but on the direction of the biological network.