Why are we required to maintain an odd number of voting disks?

Odd number of disk are to avoid split brain, When Nodes in cluster can't talk to each other they run to lock the Voting disk and whoever lock the more disk will survive, if disk number are even there are chances that node might lock 50% of disk (2 out of 4) then how to decide which node to evict. whereas when number is odd, one will be higher than other and each for cluster to evict the node with less number