Now that we have invented a way to bring new coins into the system in a steady and predictable way, we need to come up with a system to keep a list of all coins created. Why is that? Because since it’s digital, existing means just being written somewhere. It’s the difference between a jpg written on your drive compared to a polaroid pinned to a corkboard.
That’s not difficult, we could make every miner write down the coins they receive, and then just write off the ones they spend, for buying food for example. But if that’s the case, how can everybody else playing the game know that they’re not cheating, creating coins out of thin air? But even solving that issue, where do we write down when they’re are sent to someone else? On the sender’s list of coins? On the receiver’s? On both? What happens when there’s lots of players and lots of coins? This gets very complicated very fast.
The solution is to keep just one list, with all the coins created from the very first and counting. Such list should say “Miner X won and therefore gets 6 coins.” and then lots of lines that look like “Miner X gives 4 coins to player Y”, “Player Y gives 3 coins to Player Z” and so on.
And the way we can be sure that nobody cheats with the list (which technically is called a ledger) is for everybody to have a copy of that same list, and every time someone writes to it, we all copy the changes, so we all know how many coins are in the system, that nobody got to create fake ones, that nobody cheated someone else while sending. Basically, that the math checks out.
That single, cooperative, and public list of coins is the famous blockchain.