Some were forced to work and as long as they were able to perform their jobs they lived. Others were just lucky enough to not have their numbers called. NAZI's were killing as fast as they could but it took time and the unlucky ones were murdered before the Allies were able to stop the killing. Most of the ones who survived were just lucky. A very small number of Jews were used for office work in some camps - jobs such as sorting and listing valuables seized from new arrivals. Although they were fed miserable rations, the work was less strenuous than, for example, quarrying. Also those sent to the camps very late in the war stood a better chance of survival than others, provided they were 'selected' for work and not sent straight to the gas chambers. Psychological resilience may have helped some. However, as already stated, even these prisoners needed good luck. No amount of resilience could help against the outbreaks of disease that swept through many of the camps.