I recently read this article about Clean Architecture, as I'm trying to get out of some usual OO habits (interface design everywhere, but what does it do???), and program something that describes what the system does instead of how the system is built (to paraphrase "Uncle" Bob).
Once that article gets to the use case layer, the author mentions he left users until that layer because users are specific to the application, then makes a reference (that I really don't think I got) to how if it were a board game it wouldn't have users, but it would still have all the domain objects, in his case orders and products.
But the way I see it, in a web app (some light SaaS) users are part of the domain. Imagine a cloud document store like Dropbox: they store documents, so it seems a document is definitely a domain object. But they also have users don't they? Their business involves storing documents for users, and without users wouldn't that violate an aspect of their business?
I just don't get why users aren't considered part of the system in the same way documents or other things are. Can someone clarify this principle and the reasons behind it for me?