It was folly, therefore, and error, and blindness, and, as Cicero says, ignorance of facts and causes, which introduced the names of Nature and Fortune. But as they are ignorant of their adversary, so also they do not indeed know virtue the knowledge of which is derived from the idea of an adversary. And if this is joined with wisdom, or, as they say, is itself also wisdom, they must be ignorant in what subjects it is contained. For no one can possibly be furnished with true arms if he is ignorant of the enemy against whom he must be armed; nor can he overcome his adversary, who in fighting does not attack his real enemy, but a shadow. For he will be overthrown, who, having his attention fixed on another object, shall not previously have foreseen or guarded against the blow aimed at his vitals.