To keep the ledger unified, Bitcoin follows the longest proof-of-work chain principle, for which the longest blockchain ledger prevails.

Mining is the collective action of the miners in the entire network. When all miners are mining, is it possible for multiple miners to mine new blocks at the same time? The answer is: Yes (in small probability). If more than one miner mine a new block at the same time, who would be awarded for the block mining?

Let's take Bitcoin as an example. The Bitcoin ledgers are distributed all over the world. To keep the ledger unified, Bitcoin follows the longest proof-of-work chain principle, for which the longest blockchain ledger prevails. In his book titled “Bitcoin: A Peer-to-peer Electronic Cash System”, Satoshi Nakamoto wrote that “The system itself requires very little infrastructure. Information spreads across the network as best as possible, and nodes can leave and rejoin the network at any time, using the longest proof-of-work chain as proof of transactions that occurred while the node was offline.”

Suppose that two miners A and B simultaneously mine the block numbered N, at which point the blockchain forms a brief fork, and further suppose the block mined by Miner A is called Chain A, and the block mined by Miner B is called Chain B.

At this point, miners at other nodes may receive a new block from Miner A, or they may receive a block from Miner B, and then they will respectively extend the blockchain after receiving new block. As soon as a new block is mined from Chain A or Chain B, the other chain is discarded according to the longest proof-of-work chain principle. The block on the discarded chain is also called orphan block.

The blocks mined by the discarded chain are also valid until the winner is determined, and there is also a block reward. After a certain chain is determined to be the longest valid chain, the other chain becomes a discarded chain, and the reward on the discarded chain will not be recognized. Thus, the sooner a miner releases a new block, the better.

However, this is only as a knowledge supplement, in the actual mining process. As all miners mine through the mining pool, each participating miner is distributed the reward in proportion to the hashrate so there is no possibility of not getting a reward from mining a block that become an orphan block later.