Imagine a 10 foot circle around you.
Now gradually collapse that circle in towards you until you feel that it's too
close and actually feels confining. For most people, it is about the length of
your arms. This is called your personal space. When anyone gets within that
space, the short hairs on the back of your head better be going up, and you'd
better be ready for anything
The more you train your senses, the more you become aware of how easy it is to
close the distance for an attack, the larger your circle gets.