let's say you have an object like this when you started: {count: 10, etag: 1}. then for some reason, something failed.
when you retry and load the object, you get {count: 12, etag: 3}. how do you know if your previous attempt had successfully persisted or not, or if the updates to the object came from other processes/requests?
you're mixing up conflict handling vs. idempotency
Look up the two general problem on youtube. Unless the entire end to end operation is wrapped inside a giant transaction, no system in the world can give you the confirmation.
Imagine this: you issued a write, a few things can happen: 1. The callsite crashed, maybe due to an out of memory issue or whatever. You don't know if it succeeded
2. The database returned an acknowledgement, but then the callsite crashed before storing the acknowlwedgement for the next step.
Ah, the system is not capable of giving you a confirmation that your update succeeded, you don't really have a way to know without external "checkpoint" system?
Anyway, okay, I get that I don't get it, and I get that it does sound terrible, agreed!