What I would submit is that most fear is related to our fellow humans, specifically the fear that they will hurt us. This, of course, is an eminently valid fear. Especially in recorded history, there have likely been 100 people killed by other people for every one killed by a shark, a bear, a tiger, or wolves. Other humans are the most fearsome predators we face.
Shame is bowing your head, like we see dogs do. Shame is telling other people you present no threat, because you submit to them. Shame is surrender. Thus: fight, flight, and surrender all originate in the same neurological place.
Surrender is not in my nature, most likely specifically because I always feel an underlying sense of unavoidable shame which I cannot get away from, which has no cause in my present behavior, and which causes me emotional distress.
I have speculated in the past that the best soldiers are most likely those who have endured humiliation and degradation, as is the pattern in our military indoctrination.
I will add to this the discovery that those who have suffered mild to moderate developmental trauma seem empirically to have much higher pain tolerances which, combined with greatly lowered emotional sensitivity, make for the qualities we value in those whose task is enduring hardship, and working hard to kill other human beings.
I was told once, by someone in a position to know, that most of our best soldiers are sociopaths. War is insane, and in an insane world, only the insane truly belong and thrive. We need these people, but as we saw in Africa with the murder of the Green Beret there–someone who evidently retained his moral compass, making his companions deeply fearful of what he was going to say–we need to keep them on a tight leash.