Books that explore morale – e.g. in the face of overwhelming odds, high morale, demoralisation, etc. Preferably novels, not self help books.

Am re-reading the 2nd instalment of Three Body Problem and without spoilers there is a theme to do with morale.

I also remember the Stalingrad chapters from Life and Fate having similar qualities; it's also a central theme for Samuel Beckett, Tolstoy and many other writers.

Wondering if anyone out there has recommendations of books that go there in interesting ways.