Since it is impossible to generate all essential facts in a hypothetical exercise, it is evident that the more detailed our account, the more illusory it becomes. We may make any number of tacit assumptions, and develop an analysis that in the end might not be relevant to one case in a hundred. Reasoning of this kind may still be useful to train our judgment, of course. But it is clear that such an analysis can never be satisfactorily refuted by equally arbitrary arguments. If we are contentious we won't be able to reach an agreement; if we honestly seek a solution we will eventually fall into a disagreeable state of perplexity, in which we might almost despair of the validity of any theory whatever.
Clausewitz, of course, is thinking of hypothetical exercises in military strategy (he had been asked by a friend to give his analysis of two such hypothetical scenarios); but it might be applied, mutatis mutandis, to other analytical uses of hypothetical scenarios, such as many so-called 'thought experiments' in philosophy.