Everyone including Christians: what's your opinion of my Christian friend's mental state?

My friend is reading a book that talks about a plague in Africa back in the 1800's or so. Apparently there was a missionary who was able to care for the sick people, but he never got sick even though everyone else did. My friend read about this guy and decided that his immunity was due to faith in god. My friend feels bad that he himself does not have enough faith to survive the plague. I can see the self-loathing in his eyes even. Is this a normal reaction?