If someone buys a bottle of water for $1, that person cannot spend the same $1 to buy a can of coke. If a person is free to double-spend a dollar, money would be worthless since everyone would have unlimited amounts and the scarcity, which gives the currency its value, would disappear. This is called the double-spending problem. With BTC, double spending is the act of using the same Bitcoin more than once. If this problem is not resolved, BTC loses its scarcity and cannot be used to facilitate a trade between two untrusting parties. The Bitcoin Core network protects against double spends via a consensus mechanism. To explain how the Bitcoin consensus mechanism works, we first describe the concepts of PoW (Proof-of-Work) and mining.
As explained earlier, a miner needs to solve a difficult mathematical puzzle ahead of other miners in order to receive the role of being a builder of the current new block and receive a reward for doing the work. The work of resolving the...