vulnerable point

"Just the other way," retorted Lorenza, delighted as angry persons are at having found the antagonist's vulnerable point.

Every variety of danger was arising at once; the tempest was concentrated upon the vulnerable point; destruction was imminent.

Can it be the only vulnerable point, which would necessarily determine the thrust of the lancet?

The sting, I am told, is directed at one point rather than another because that is the only vulnerable point.

In love and battle, every peril should be avoided; every vulnerable point made impregnable.