Two events arrive out of order. You don’t know they’re out of order. You process them anyway. The system ends up in a state that never should have existed. Sequence Numbers as the Foundation A global sequence number assigned to every write event is the most direct solution to ordering problems. Event 1, event 2, event 3. If event 4 arrives after event 6, you know something is missing. You wait, or request a replay, rather than blindly processing forward.