Once a soldier gives up the idea that everything will be ok, and accepts whatever it is they have to do, which is up to and including dying, then they'll be able to fight as long and as hard as they have to. And they won't break down mentally, or suffer from fear, or despair. And then, almost paradoxically, they will greatly increase their chance at survival, and not just in terms of living, but in terms of being mentally healthy, and happy. And this rule, that you have to accept everything, and do whatever you have to do, doesn't just apply to war. It applies to all of human life. When people stop questioning, and despairing, and self pitying, and feeding into their fear, and when they simply get on with it, as best they can, that's when they'll have their best chance at a good life.