You bring up an interesting question. For me, it is when I begin to become mentally uncomfortable. By this, I mean that I begin to have the feeling that something is not quite right, or someone is not quite right (including myself). For example: If I am expecting a landmark on a trail, and I don’t come to it when I expect, I begin to feel mentally uncomfortable. Sometimes I might be speaking with someone I have never met before, but for whatever reason, I don’t quite trust them. Or (for myself), I might be feeling the first signs of an illness.

In all the above examples, I may continue on for a bit, but I start to think about contingencies. As I continue on, if something continues to nag at me, I try to do something about it. Re-verify my position on my map, put some distance between myself and the person I am speaking with, or try to determine how sick I am about to become and pre-position myself accordingly (home vs. hospital, etc.).

My “inner voice” or “trusting my gut” or whatever you want to call it has kept me safe in some situations that could have been very very bad. I can think of at least two situations that my “inner voice” kept me from getting lost, thereby preventing me from having to be out unexpectedly overnight, thereby preventing a “survival situation”. It seems especially fine-tuned when dealing with people, but that may be influenced by profession and its experiences.