1. Quorum & Split-Brain Prevention: Galera uses strict majority voting (quorum) to guarantee consistency. In a cluster of $N$ nodes, a partition must control more than 50% of the votes ($\lfloor N/2 \rfloor + 1$) to remain in the "Primary" state and accept writes. 2. The Partition: In a 2-node cluster ($N=2$), the majority threshold requires at least 2 votes. If a transient network glitch interrupts communication between Node A and Node B, each node can only see itself (1 vote out of 2, which is 50%, not a majority). 3. The Total Lockout: Because neither node can prove it has a majority, both nodes immediately switch to ``non-primary`` state to prevent data divergence (split-brain). Both databases refuse all read and write queries, resulting in 100% application outage despite both servers being completely healthy.