Every blockchain requires a unified system to validate transactions and mine new tokens. This unified standard gives blockchain technology its utility as a reliable medium of exchange.
To operate a financial transaction, some blockchains require miners to show proof of work. This ensures 1) transactions are legitimate and 2) new tokens are validated. If a miner can’t prove their work, the transaction can’t be completed.
Under a proof-of-work model, blockchains rely on complex mathematical puzzles to validate new blocks. These systems prevent malicious actors by preventing the use of holdings more than once, or the use of fraudulent tokens.
In blockchain tech, each token and transaction is unique, allowing for the development of a permissionless, decentralized financial system. Bitcoin is the most prominent example of a proof-of-work blockchain network. But other large networks like Ethereum also incorporate PoW.
As more blocks are validated on-chain, puzzles for proof-of-work become more complicated. The consensus algorithm adjusts over time based on collective computing power. The system is designed to keep block production rates stable. Otherwise, new tokens would be rendered worthless.
In this light, it is not easy to mine popular coins. While over 90% of all Bitcoin is mined, many experts like @Waltzinthestreet believe the remaining 10% will never be collected in our lifetime. This is due to the complex nature of the work required to mine the remaining blocks.