From New York Times:

Instructors repeatedly told me that a big part of their job was to make people feel vulnerable, to make them aware of dangers they were not conscious of before to understand that bad things can happen at any time. One instructor told me he encourages students to carry their gun at all times. If students say they plan to leave it in the car, he responds, “So what you’re telling me is the only time you are ever going to get attacked is if you are in your car?”

The instructors describe a world teeming with violent and deranged individuals. And not just any individuals. The scenarios cluster around the public spaces of racially diverse cities. “More often than not,” an instructor who had been a high-ranking police officer said, the place you’re likely to be attacked is “in an urban part of society.” Another instructor, also a former police officer, tells students to keep their gas tanks filled at least halfway to avoid situations in which “it’s the middle of the night and you need to get gas in downtown Houston.”