I said it somewhere else, but I'll say it again here. Hope is a dangerous thing for Jack right now. He's gone so long without it that if he lets in just a little, even that might be too much. He's like one of those people who have suffered from extreme starvation. You can't let them eat too much because their bodies won't be able to handle it and will make them expel the food. Likewise, if Jack lets himself hope too much too soon and he gets disappointed, I don't think he'll ever recover.