It's also really hard. Trying to determine how to split up any code base into logical divisions such that you when adding the next 5 years of functionality you

It's also really hard. Trying to determine how to split up any code base into logical divisions such that you when adding the next 5 years of functionality you'll have the fewest number of cross division processes is hard. This is why Martin Fowler recommends starting with a monolith and refactoring into microservices unless you have extensive experience building out very similar applications in the same domain.