What if the feature/module designed has to interact with other parts of the system? I saw that all the time, it's really hard to identify the right partitions

What if the feature/module designed has to interact with other parts of the system? I saw that all the time, it's really hard to identify the right partitions in a system. It requires a lot of research and experience. Whenever one of those partitions is missed/overlooked, the software gets muddy and hard to work with around that area. When brought to the extreme where very little boundaries were identified, this is common in CRUD apps where entities are confused with partitions the entire time, every change to the code ripples from the database all the way to the frontend. In Rails world, this is a highly common problem: a change to database schema affects the UI directly, so every time something is changed in the schema, the following has to change: - JSON renderers - React or HTML views - db schema Even for additive changes