Bob, possibly a Fallen Hero or Atoner, refuses to fight any longer. He decides he would rather become an Actual Pacifist or Technical Pacifist, or retreat from the world all together. The reasons for this vary. Perhaps Bob now has (or gave someone) a Dead Little Sister, or maybe they just think their Quest has come to an end (though their opponents probably would beg to differ.) They may have simply met the one person who could convince him that murder is not always the answer. It could be a simple case of being beaten so badly and so often that they just give up completely.