The best way I have learned to explain to others is this quote from this article:
https://blog.chain.com/a-letter-to-jamie-dimon-de89d417cb80The paper proposes a solution: form a peer-to-peer network. Make it public. Announce your transaction to everyone. In your announcement, point to the specific funds on the network you want to spend. Cryptographically sign your announcement with the same software key that is linked to those funds so we know they’re yours.
It almost works. We need one more thing: a way to make sure that if you broadcast two competing announcements (that is, if you try to spend the same funds twice) that only one of your attempts counts.
Bad solution: designate a party to timestamp the transactions and only include the transaction that came first. We’re back to square one. We have a trusted intermediary.
Breakthrough solution: let entities compete to be the “timestamper!” We can’t avoid the need for one, but we can avoid designating one in advance or using the same one for every batch of transactions.
“Let entities compete.” Sounds like a market economy. What’s missing? A reward for winning. An incentive. An asset.
Let’s call that asset Bitcoin. Let’s call the entities competing for the right to timestamp the latest batch of announced transactions “miners.” Let’s make sure anyone can join this contest at any time by making the code and network open.
Now we need an actual contest. The paper proposes one. On your mark, get set: find a random number generated by the network! The number is really, really hard to find. So hard that the only way to find it is to use tons of processing power and burn through electricity. It’s a computing version of what Veruca Salt made her dad and his poor factory workers do in Willy Wonka. A brute force search for a golden ticket (or in this case, a golden number).
Bitcoin Mining
Why the elaborate and expensive competition to do something as simple as timestamp transactions for the network? So that we can be sure the competitors have incurred a real financial cost. That way, if they win the race to find the random number and become the designated timestamper for a given batch of transactions, they won’t use that power for evil (like censoring transactions). Instead, they will meticulously scan each pending transaction, eliminate any attempts by users to spend the same funds twice, ensure all rules are followed, and broadcast the validated batch to the rest of the network.
Because if they do indeed follow the rules, the network is programmed to reward them…
… with newly minted Bitcoin, plus the transaction fees, denominated in Bitcoin, paid by the senders. (See why they are called miners and not timestampers, now?)
In other words, miners follow the rules because it is in their economic self-interest to do the right thing.