Bitcoin miners repeatedly hash block headers while searching for a result below the network target. A successful miner can propose a candidate block, but every full node still checks that block against Bitcoin’s rules.
What proof of work proves
Proof of work makes producing a valid block computationally expensive. It does not give miners permission to create invalid transactions or ignore the supply rules enforced by nodes.
Nodes still enforce the rules
Proof of work chooses between valid candidate histories; it does not make an invalid block valid. Independent nodes reject blocks that break the rules they enforce.
Why difficulty changes
Bitcoin recalculates its mining target every 2,016 blocks. If blocks arrived faster or slower than the protocol’s intended pace, the target changes to move future production back toward the expected interval.
Difficulty follows block timing, not market price
The adjustment uses the time taken to produce a block interval. Price and mining economics can affect hash rate indirectly, but they are not inputs to the protocol calculation.
Sources
Educational information, not investment advice.