Brain Pickings has it covered. Do go visit. Two quotes:
“Doubt and mistrust are the mere panic of timid imagination, which the steadfast heart will conquer, and the large mind transcend.”
"Optimism that does not count the cost is like a house builded on sand. A man must understand evil and be acquainted with sorrow before he can write himself an optimist and expect others to believe that he has reason for the faith that is in him."