> You design systems to make them self-correcting: Log events durably first, and then act on the events. If possible, make operations idempotent. If not, either make operations fully commutative, or group them into larger commutative operations and use local transactions (so require local consistency) to ensure they are all applied at once. The point is not to require no atomicity, but to localise any guarantees as much as possible, because the more local they are, the less they affect throughput.

You can't do this in general, because we often want to build applications where the user expects their actions won't be reordered. People often forget this: the user is sort of the unstated extra party in a distributed system. A canonical example is privacy settings on a social network. If I want to hide my profile from a user by unfriending them and then post something unkind about them, it doesn't really work for me that the application is free to reorder my actions.

At some point your desire to have HA via a weakly consistent system conflicts with intuition and usability of an application.