In a distributed system, partitions cannot be avoided, and when a partition occurs, we must choose between consistency and availability. In Figure 3, n3 goes down and cannot communicate with n1 and n2. If clients write data to n1 or n2, data cannot be propagated to n3. If data is written to n3 but not propagated to n1 and n2 yet, n1 and n2 would have stale data.