A friend walks in. A delivery driver knocks. A stranger says hello on a walk. And your dog won't stop barking, even five, ten minutes later, long after the "threat" has clearly done nothing wrong.
This is called trigger stacking, and it happens when a dog's nervous system gets so activated that it can't process new information calmly. Every new person becomes another alarm bell, even when nothing bad is actually happening.
Dogs that react this way to new people aren't being "protective" or "stubborn." They're living in a state of chronic hyper vigilance.
Their nervous system has learned that new = danger, and it can't tell the difference between an actual threat and a friendly guest.
This affects their ability to socialize, your ability to have people over, and their overall quality of life.
If your dog can't settle within a few minutes of meeting someone new, their nervous system needs real support, not just more exposure or more corrections.