So I've seen this pop up in several Lets Play videos and I recognize it's an important facet of the game, but I feel like I'm missing a couple things. First of all, how do you create them? I've messed around with the title system for the past couple days but haven't had any luck so far. Secondly - what's the importance of keeping the de jure duchy borders? I keep hearing this brought up too, which made me wonder if it's possible to add or remove counties to the duchy itself. And last of all I always see people on the forum talk about giving duchies over to their heirs. Is this something you should always do? It was my understanding from most the videos I watched that you should use them as an incentive to keep your important vassals loyal, but maybe I'm oversimplifying it.