how does gerda use her imagination to survive the war

All But My Life is the incredible true story of how Gerda Weissmann Klein survived the Holocaust. One of the ways that she was able to achieve this was to focus, not on the horrors that were happening in front of her, but on the past and on the future. She imagined good things that had happened in her past, such as remembering her old house and spending time in her garden. She also looked forward to a future in which she could get married and have children and live a normal life. She even thought about what color dress she would wear to parties to keep her mind occupied.
She often imagined and hoped that somehow, on the next stop of the trains she rode on, she would see her family members again. Although imagining these things didn't lessen the dire nature of her situation, they did help her to stay mentally focused on life instead of death. In a quote from Teaching Tolerance magazine, Klein says "I was fortunate not to be a realist, because I saw far too many realists in the camps who did not survive."
https://www.tolerance.org/magazine/fall-2005/here-to-tell-my-story