Can someone suggest, perhaps ELI5, how it isn't possible for a miner to see a transaction payment to themselves; duplicate it many times; and put those into a block that they confirm? That would be trying to suck the donating account dry, down to the modulus. How is each transaction unique, that miners cannot exploit them in the block they are creating? Obviously, trying that would still be a matter of luck in order they are the miner confirming the next block but still not clear to me, how it's not possible. I'm expecting that transactions can't be duplicated from one block to another because of some ?Merkle root signature of the existing tree or similar but how is in-block duplication prevented?
If a miner tried to duplicate payments in the block it would be invalid and the block would be ignored by all the other miners.
