Ever take up boxing ? If not, then understand that boxing is a rigged sport. I do not mean that fights are rigged to set winner/loser but that the fighters are set to be as parity to each other as possible. The weapons -- fists -- are padded to minimize physical damages. The entire fight is time limited. The fight is segmented (rounds) to allow respite. There are rules limiting the fighters as to where they can target -- no hitting below the belt. If one fighter is incapacitated or seemingly so, he is allowed time to recover -- the 10 count. Then if there is no clear victor, there are judges to rule victory.
War is not so clean. But to use the boxing analogy, if your opponent punch you in the ribs, that does not mean you respond in kind. If there is an opening to the jaw, you bear the punch in your ribs and hit his jaw. You attack my national asset, it is my burden to teach you a serious lesson and the severity of that lesson depends on how my nation feels about what you did.