The whole point of the work is that courage and optimism go hand in hand and are necessary to overcome seemingly insurmountable obstacles. The horrors of the holocaust serve as the background for the story and serve as an opportunity for this unique young woman to display her strength, which will outlive her and inspire future generations.
Whether it is in her self-talk, repeating the mantra of "everything is alright," or in declaring how much "better" she and her family have it than those who are not "lucky" enough to be inside the annex, the optimism springs from within. Her strength of character shines through on every page.
Imagine yourself forced to live in hiding, cramped into a space not suitable for human habitation, but taking the time to decorate and make it into a "living space."
Can you not hear it in her words, "I have often been downcast, but never in despair; I regard our hiding as a dangerous adventure, romantic and interesting at the same time"?