Thus the new code allows us to determine whether an error has occurred, but no more. This is a prototype of an error-detecting code. When we receive an ambiguous message, we simply ask headquarters to send it again
An error-detecting code is fine as long as errors do not occur too frequently. Otherwise things may get out of hand. Even our message requesting headquarters to resend theirs may contain an error, and messages will be going back and forth for quite a long time, enough for us to lose the war.