Blockchains are created on the basis that there is general agreement on the protocol by every participant. This is known as consensus rules that govern the protocol on a blockchain. The root word of consensus is “consent”, which means that even if parties disagree, there is overall consent to move forward in order to resolve any disputes.
Consensus protocols are used by nodes to agree on the blockchain content. All nodes must agree to the network verified transaction being permanently incorporated into the blockchain. The goal of consensus rules is to ensure a single chain is used and followed by every participant on the network without the need of a central trusted authority. If a major disagreement ever occurs on the consensus protocol, this might potentially result in a hard fork, thereby creating a split in the blockchain into two separate chains.