In the intro to the "Crack Up", there's a quote which I used a a mantra

The ability to hold two conflicting thoughts and yet continue to function is a test of intelligence - be able to see that things are hopeless and yet be determined to make them otherwise.

You don't need to lie yourself that the world is not falling apart, but being truly optimistic instead of nihilistic at the face of that is a difficult test for any intelligent human being.

In the scale of the universe and history, most of what you do is not important, but it is very important that you do it (rambles on about Gita, Ecclesiastes and Plato ...).

Pessimism of the intellect, optimism of the will