… And I seem to have such strength in me now, that I think I could stand anything, any suffering, only to be able to say and to repeat to myself every moment, ‘I exist.’ In thousands of agonies―I exist. I’m tormented on the rack―but I exist! Though I sit alone on a pillar―I exist! I see the sun, and if I don’t see the sun, I know it’s there. And there’s a whole life in that, in knowing that the sun is there.

— Dmitri Karamazov to his brother Alyosha, The Brothers Karamazov, Fyodor Dostoyevsky