I would be extremely careful. ISIS sex slave victims such as Nadia Murad (who was raped repeatedly in a brothel for almost a year) would beg to disagree with you. As do many Holocaust victims who lost faith in God. Hell Hitler been through the hells of war but he became a huge cynic after the war and same with Benito Mussolini (who was judged as the bravest soldier in his unit in WW1).

How about the fall of the Roman Empire? Where hardened Roman warriors gave up and just let the barbarians enter the city without a fight despite decades of war experience?

In reality for much of history "hope" does not change the outcome. If that was true, the Crusaders would have kept Jerusalem. Neither does pessimism means shelter or defeat-the Calvinists would like to have a word with you as do the militia who fought the Vikings for decades (and often believed its the end of the world and God is punishing mankind so all their hard fighting and work is pointless in the end).