Well I don't think he was saying "cut and paste this exact code into your codebase" but rather that it is possible to write safeguards such as this... in this c

Well I don't think he was saying "cut and paste this exact code into your codebase" but rather that it is possible to write safeguards such as this... in this case, perhaps checking whether an account has already been billed this month, or whether there is already a transaction pending, or... We can't prevent every mistake but we can make sure the same one doesn't happen again.