Human survival instinct is very strong, and here's another story to prove it:
A man was using a chainsaw, and it kicked - back.
{for those of you who have never used one, when cutting, you should try to avoid using the tip of the 'blade' or the motion of the chain rotating around it could force the blade towards you quickly - I had this happen to me once, and if I weren't wearing special protective chainsaw pants, I probably would have cut myself on the leg}
The blade came up, it struck him on the neck and dug in fast, nearly decapitating him.
Instantly he dropped the chainsaw, and
while holding his head on with his hands walked towards help.
This is an illustration of what a person is capable of in life - threatening situations, and also of the strength of the individual's survival instinct.
I believe that people who find themselves in these situations go into 'survival auto - pilot' mode where normal modes of thought don't come into play at all, and that's what gets them through.