Not really theory, but one of my favorite quotes:

Go forward knowing that, sooner rather than later, the great avenues will open again where free men will walk to build a better society.

When this speech was broadcast there were audible bombs and gunfire in the background, and and he (Allende) was murdered shortly after. The fact that he could display this level of hope under those circumstances is still amazing to me and is something I think about whenever my doomer brain starts acting up.