How are sisters, Ami and Olive, different in the novel, The Unhoneymooners?

Olive struggles with finding a sense of self-assurance in her actions. Olive allows the world to be defined for her and lets herself be defined by what she feels is her never-ending bad luck. What adds to this sense of negativity is the fact that her twin sister, Ami, is the complete opposite: full of optimism and good fortune. Since they are twins, Olive believes that she is defined by her differences to Ami.