Communications Failures
Secondaries can’t distinguish a primary failure from a communication failure that partitions the network.
If the secondaries elect a new primary and the old primary is still running, there will be a reconciliation problem when they’re reunited. This is multi-master.
To avoid this, one partition must know it’s the only one that can operate, and can’t communicate with other partitions to figure this out.
Could make a static decision. The partition that has the primary wins.
Dynamic solutions are based on Majority Consensus