Understanding Proof of Work Mining
The Challenge: Find a nonce (number) that, when combined with block data and hashed, produces a hash starting with a specific number of zeros.
Why It's Hard: SHA-256 is unpredictable - you can only guess and check. More leading zeros = exponentially more guesses needed.
Chain Integrity: Each block contains the previous block's hash. Changing any block invalidates all subsequent blocks, requiring re-mining of the entire chain.