Many of us develop a built-in radar from bad past experiences. An older man, a stranger, attacked me when I was a first year college student, out in the street about eight at night. I got away, luckily, with minor damage, but ever since that experience I watch everything and everyone very carefully, especially at night.

The shape of someone approaching from a distance at night can be informative and the gait, too, because they can reveal if the person is drunk, angry and so on. These are important skills, in my opinion, though it would be nice not to have to have them.