Due to the difficult conditions and the need to fight for survival, which prisoners does Frankl claim were most likely to survive life in the concentration camp?

Frankl writes, "On the average, only those prisoners could keep alive who, after years of trekking from camp to camp, had lost all scruples in their fight for existence; they were prepared to use every means, honest and otherwise, even brutal force, theft, and betrayal of their friends in order to save themselves. We who have come back, by the aid of many lucky chances or miracles -- whatever one may choose to call them -- we know: the best of us did not return."