Why is the Night King doing what he's doing? Unlike the undead he commands in his army, he seems to have motivations for his actions, and we'd like to learn more about them. For instance, why did he take out Viserion rather than Drogon when he had a clear shot at both (and Drogon's death would've lead to the death of many of the humans Drogon lead to safety)? Is this all the ultimate revenge mission after the Children of the Forest forced him into his icy immortal state? Or is there something more to it? If the Great War is to be the one of the final season's greatest focuses, we need to understand more about this side of the fight (aside from the fact that they're death incarnate).