So lets say you have a character who is on the run from a particularly powerful organization. Over the course of the story he becomes more and more desperate, and begins committing more and more morally questionable actions. It's only his wellbeing that is at risk, and he's not out to help some greater cause or anything like that. Early on he would occasionally help people in need, but as he got more desperate he would help people less and less and even begin hurting, or taking advantage of, people weaker than him in order to escape. At what point, or what action, would be going to far for you, when you could no longer root for this character.