If any (No)SQL database contains a mistake, you can either fix the mistake or change the program working with the data to either ignore or override the mistake.

If any (No)SQL database contains a mistake, you can either fix the mistake or change the program working with the data to either ignore or override the mistake. Smart contracts are running on an immutable database, the blockchain. If anything is landing there because of an error in the contract, you will never get the mistake out. It's engraved forever. Updating a smart contract should never happen because once you can update it, you can change its contents and its rules in a way that might benefit only one side. Even if you create rules to update the contract, finding 100% consensus (everything below 100% is unacceptable if you are explicitly using smart contracts to disallow cheating) to update the contract takes time in which more mistakes might happen and make the whole contract unusable.