Comment by srkiNZ

> why can't I choose to view "the system itself" as the thing that is on the other side of a de-duplicator?

because the "de-duplicator" would either:

* be somewhere else on an unreliable network (in which case we have the same problem)

* be on the same machine (or in the same process) as "the system itself" (in which case from a distributed systems perspective makes it the same thing)

> It seems a bit pedantic...

It is pedantic. The only reason that these "delivery" rules are popular is because of how many times programmers have gotten it wrong. Mostly by making assumptions that either:

* the network is reliable

* the message queue (or whatever) will de-duplicate messages for me