What metaphors are used in Doomsday Book by Connie Willis?

The Optimism of Youth is both theme and metaphor. When Dunworthy is warning Kivrin of all the things that could go wrong, Kivrin is thinking only of the experiences that await her and that Dunworthy is only trying to keep her from those experiences. Kivrin's thinking on this point is the same as many other young people, and it's Mary Ahrens who reminds Dunworthy of this fact. Mary tells Dunworthy that she herself, as a young woman traveling with her sister, had barely missed a quarantine and traveled through a war-torn country in order to reach a specific destination. She says that looking back, she can see the danger, but at the time she saw nothing but the ultimate goal - and she reached it safely. Mary points out that Kivrin is in this same frame of mind and that she, like Mary, will likely return unscathed.