Split-brain corrupts data quietly. This is how Raft gets N crash-prone nodes to agree on a leader, a log, and a lock — and why a majority is the only quorum that can't lie to itself.
Everyone can recite 'Raft elects a leader by majority.' The hard part is the log — how a follower that missed writes during a partition gets repaired, and the one subtle rule that stops a committed entry from ever being lost. Drive a live 5-node cluster, then take it apart.