
It's been a long ride. These two have done everything they can to stay alive. But apparently, that just wasn't enough. At this point in living, the man and the son don't really have anything. Aside from a little food, they don't really have anything to loose. But they keep going. Why? They haven't eaten in days and all odds of long term survival al completely gone. So why do they keep going?
Everything in life is done to achieve something. In a world like this, there is little more that they can achieve. And even if they are able to survive through something, there will be something else waiting for them to hold them back. So why keep going? I answer this with one

phrase: It's all about the mentality. In just about any world, there will be obstacles to overcome as well as struggles. Their mentality consists of doing the same thing in this world that they would in any other: keep going because they have nothing to loose.
However, these are especially hard times that they have to go through. They need a new set of ideas to move forward. They need something a little more inspirational to keep going. They need to remind themselves that being human means to prevail and endure even if they know there really is no light at the end of the tunnel. So the really answer to why they keep moving is to demonstrate that they are human and when you have truly nothing to loose, then just keep carrying the "fire inside you (116P.).