Exactly! Adam, you say "There is no such thing as overall usability of a system: it is a sum of the usability of the given scenarios played out." and I respectfully disagree! The overall "usability" of the system relies on the understandability of the system, and THAT relies on how much the conceptual model of the system aligns to the users mental model of the problem domain. Can a user come into this digital system and easily identify the things they care about? For a teacher using edtech software, can they easily see and find Students, Classes, Lessons, Tests? Do the connections between those digital things reflect how they connect in the real world? Can I navigate to a class and see all my students in the class? Can I navigate to a student and see all the lessons they have completed? Can I do what I want to do to these objects? Can I reassign a lesson to subset of students? And can I clearly see the information that I care about for each object? Can I see a student's score for a lesson and the class average score? Design the most usable flows ever, but if they are not acting on clear, valuable, recognizable objects, you are fighting an uphill battle. Think of it this way, in any physical environment, it's impossible to act until you know what and where the things are in that environment. And in SO MANY digital systems, us designers do not make that immediately clear to our users. If the digital objects and relationships are clear (and obvious based on the real world) you've just flattened the learning curve and reduced cognitive load. If you need more convincing, check out ooux.com/testimonials 🤓 💅🏻