What Is the ‘Longest Chain Rule’ in Proof-of-Work?

The longest chain rule is the fundamental consensus mechanism in PoW blockchains like Bitcoin. It dictates that in the event of a temporary fork (two valid blocks found simultaneously), the network's nodes will always accept and build upon the chain that has accumulated the most proof-of-work, which is typically the longest chain.

This rule ensures all nodes eventually converge on a single, shared history.