Got it in one - "because the protocol says so." There are circumstances which allow us to give up - or not even attempt - resuscitation. There are others which offer us no option (eg: CPR in progress when we arrive, cold water drowning, victim is pregnant). When in doubt, though, we do it. It is the defensible option. What Tom and his mate saw here on the ECG was VF in a pulseless patient; that is a shockable disrhythmia, and, from there on, you are commited. If the effect of shocking such a patient is to turn the VF into asystole, we are expected to make heroic efforts on behalf of the patient, but are permitted the discretion of eventually giving up. This is not a decision we make lightly; unfortunately, though, it is the one we make most often