We learned that if we saw an X with a square around it, we should not enter. It's unsafe. If your job is to help search for others and you get hurt and can no longer search, how much help would you be? It's taken me years to realize this lesson applies to how we take care of ourselves in our own lives.
I have run into at least 10 people recently who have stopped on fast-moving, heavily-populated sidewalks to take a #selfie. There is no historical building behind them, no beautiful landscape, no real reason to take a picture of themselves other than the fact that they can reverse the camera on the phone, gaze at their own visage, and then share it on social media so the rest of the world can gaze upon it as well.