This is one of the discussions about human instincts. For that matter, it is the most powerful of our instincts. It is our Survival Instinct. You don't often hear about instinct because in the West, the influence of the Church demanded that humans were a divine creation rather than an animal. If we had instincts, that would mean we were animals, not divine. Well, we have very powerful instincts and they both drive you and inhibit you to protect you from harm. Your survival may have been the main focus of evolution for the last 10,000 years. You need to know about your instincts but without a name for them, you can't think about them much or communicate about them. We do have a name for Survival instinct though. It's just sort of hidden. The word is "Faith" and it has been claimed by religion but really, it is any unsupported belief, not just a belief in a God. It is the unsupported belief that you should survive. It is why you strive to survive and it is as powerful as religions claim. It makes humans hard to kill. It is also what makes you decide between right and wrong, not how, but why. Learn to see it in yourself and it will strengthen you as well as give you understanding. Learn to see it in others and it is revealing.
I figure this is a 7, so I may replace it when I get the time. Still, it tells the story.