Every miner expects every other miner to mine of the longest chain and as a result every miner mines the longest chain. This means that if a miner is working on a chain and then sees another longer chain, then they should immediately stop working on the shorter chain and start working on the longer chain.

The result is blockchains utilizing Nakamoto Consensus are mutable by design and there can be no transaction finality since the chain history could potentially always be overwritten by a longer and therefore legitimate chain.