The sixteenth zone needs to have something of its own. A home, a car, an object a person is attached to — what matters is not the size but the fact that it belongs to them and is disputed by nobody.
The other half of the zone is the past. Such a person trusts what has been tested by time: school friends, old relationships, things with a history. They accept the new slowly, and not because they are conservative, but because they lean on what has already held up.
Hence the vulnerability: losing what is one's own — a home, a possession, a person known for years — is lived through more heavily than it looks from outside.
The best state arrives when the sixteenth zone has a place from which nobody can ask it to leave.