It is more sensible to be pessimistic; disappointments are left behind, and one can face people unembarrassed. Hence, the clever frown upon optimism. In its essence optimism is not a way of looking at the present situation but a power of life, a power of hope when others resign, a power to hold our heads high when all seems to have come to naught, a power to tolerate setbacks, a power that never abandons the future to the opponents but lays claim to it. Certainly, there is a stupid, cowardly optimism that must be frowned upon. But no one ought to despise optimism as the will for the future, however many times it is mistaken. It is the health of life that the ill dare not infect. There are people who think it frivolous and Christians who think it impious to hope for a better future on earth and to prepare for it. They believe in chaos, disorder, and catastrophe, perceiving it in what is happening now. They withdraw in resignation or pious flight from the world, from the responsibility for ongoing life, for building anew, for the coming generations. It may be that the day of judgment will dawn tomorrow; only then and no earlier will we readily lay down our work for a better future.
“An Account at the Turn of the Year 1942-1943,” Letters & Papers from Prison