Updated: Oct 15, 2022
All living beings are afraid of death, they all seek to protect themselves and their life. Safety can be physical, but it can encompass other dimensions, extending to one's family, social conditions, historical circumstances, but also emotions and thoughts.
Usually one seeks safety by cultivating a degree of aversion against what is perceived as a potential danger. If I'm scary enough, that dangerous thing won't even try to harm me.
But aversion either overshoot or undershoot the target. How many are the potentially dangerous things? If one needs to cultivate aversion against them all, that would be hell. So aversion overshoots.
However, aversion is not even helpful to eliminate dangers. A real danger is there regardless of one's attitudes towards it. Like a trap, a poison, or a threatening predator, they don't really care if one responds with aversion or not. And if one manages to simply step outside of their domain, not falling into their sphere of activity, then one is safe regardless of one's attitude (including aversion) towards the danger. So aversion undershoots.
However, there is a sense in which almost everything can become a potential danger. Take a simple kitchen knife. Very helpful tool to prepare a meal. But if used in another way, it might become a lethal weapon. What's the difference? In the knife? No, of course, but in the intention with which it is used. On one occasion (AN 6.103), the Buddha compares all intentions and actions to a murder that follows you with a drawn sword. You can't avoid the killer, but you can remain safe if you don't let them come close enough to strike. How? By keeping intentions aloof from unwholesome basis of actions, namely, secluded from aversion, greed, and ignorance.
That's why non-sensuality (nekkhamma) is the only true safety (khema).