(...) the question to be asked is ... whether that whole sequence of events [event] is a natural and probable consequence of J's negligence and a reasonably foreseeable result of it. In answering the question it is helpful but not decisive to consider which of these events were deliberate choices to do positive acts [positive act] and which were mere omissions [omission] or failures to act [failure to act]; which act [act] and omissions were innocent mistakes or miscalculations and which were negligent having regard to the pressures and the gravity of the emergency and the need to act quickly. Negligent conduct is more likely to break the chain of causation than conduct which is not; positive acts will more easily constitute new causes [cause] than inaction.