One man had a retarded child back home he wanted to care for. Another was deeply in love with a girl he wanted to marry. Frankl himself aspired to be a writer, and was in the middle of his first manuscript when he was arrested. Frankl did survive, and has contributed greatly to our understanding of the human 'will to meaning'. In one word, the secret is what the Bible calls 'hope'.
Humans are 'hopeful beings'.
Hope means God is with us in trouble and in triumph. Resurrection hope means God is with us in life and death. Hope means the God who was with his people in the past will be with them always. Please, Lord, keep me committed to the hope that you are with me as you were with your people in the past - and will be with me forever. Where there's hope there's life.