A conversation can go from calm to tense before anyone says anything “wrong.” A slight change in tone, a pause that feels too long, or a look of disappointment can send the body into protection mode. Suddenly the goal shifts from understanding to winning, explaining, shutting down, or escaping. That shift is often called defensiveness, but defensiveness is not only a personality trait or a bad habit. It is also a nervous system response. The body detects possible threat, then