What we all have in common, is that we are not always trying to protect ourselves or others.
“…provide for the common defence,…” United States Constitution, Preamble
We walk; we move; we breathe; we adjust clothing; we maneuver items with our hands. This is all defence, for each self. Each self also can, for and as, himself or herself, provide defence for others.
(If a self pretends not to care about oneself, or to have no vested self-interest in serving others, then that blindness becomes dangerous – to others.)