The correct answer is Optimism is important to success, this can be confirmed if we take a look at the rest of the excerpt from his inauguration speech:
"This great Nation will endure as it has endured, will revive and will prosper. So, first of all, let me assert my firm belief that the only thing we have to fear is fear itself—nameless, unreasoning, unjustified terror which paralyzes needed efforts to convert retreat into advance. In every dark hour of our national life, a leadership of frankness and vigor has met with that understanding and support of the people themselves which is essential to victory. I am convinced that you will again give that support to leadership in these critical days."
This inauguration address was given by President Roosevelt at a very difficult time for the American people; the depression had reached its lowest point and Americans were really concerned about the situation, Roosevelt intended to convey the message that although there were huge material concerns the optimistic spirit of the people will be crucial for them to succeed.