I have read many books about intense trials and adventures. A favorite, Touching the Void, by Joe Simpson. Joe falls 150 feet into a icy crevasse (after making a first ascent of Siula Grande in the Peruvian Andes), breaks his leg, and somehow has the will to pull himself out and crawl back 5 miles (which took three days) to his base camp, with no food, no water, only to reach camp in a couple hours time before everyone left. HOLY CRAP. I have watched and read that book several times and still marvel at what it took to keep going.
Another favorite is the book Unbroken, by Laura Hillenbrand. I almost could not read this book yet I could not put it down. United States soldier, Louis Zamperini's B-26 plane was shot down over the open ocean and for 47 days he floated there with no food except for whatever fish and birds he could catch and what little rain water he could collect. When he found land, he was captured by the Japanese where he was tortured and starved for months. HOW DID HE KEEP GOING? How far did he reach inside himself to survive? Why didn't he give up?
The same thing can apply to those who suffer a loss. My daughter died in childbirth in 2005...how the heck did I move on? I could have easily given up and said, "fuck it, this world sucks and I was handed something really shitty". But, instead, I picked myself up and moved on. I told myself, maybe I could learn from this experience instead of suffer and dwell on it. Instead, I memorialized her and focused on getting myself well and was fortunate to meet other mothers and fathers who had experience the same loss. I gained strength from that experience, and maybe this is what others feel when they are in a tough situation. Perhaps they spark the survival instinct to get through the day to day, but in the end, it is a learning experience and a chance for someone to grow. With every experience, bad or good, we learn.