This is actually pretty well thought out here. I feel like the most important one is the one that I consider to be the most difficult: Optimizing for the most p

This is actually pretty well thought out here. I feel like the most important one is the one that I consider to be the most difficult: Optimizing for the most probable. To me, it's always a struggle between probability, predictability, and shortest possible paths between states. Probability being that at any given point, the path to what the user is most likely trying to do is as short as possible. Predictability means that from any given state, there is a consistent and predictable way that the user can know how to get to any other state. And finally, that from any state, the ability to switch to any other state in the application is as short as possible (which obviously conflicts with probability). In my mind, almost every UX should be the equivalent of tabbed, nested folders. This takes care of predictability and short paths between all application states. The area this falls behind is in probability, in that there is no effort made to guess what the user wants. Given that your average user in a large application is unlikely to care about anything outside of the given task they're trying to accomplish, I feel like it's arguably more important than the things I traditionally prioritize for, and therefore something that I have to work on the most.