Question for the book Kidnapped!!!! PLEASE HELP even if you didn't read the book!?

I did not read the book, but my GUESS is that David maintained his hope and optimism because he wanted to be reunited with a woman he loved back home (or family -- perhaps a wife and children). I'd ume that his memories of the person with whom he wanted to be reunited kept him hopeful and optimistic, and fueled his will to live.