paragraph:  From a curious scholar's lore he drew fantastics with which to torment his victim.  We heard of all the witches, warlocks, incubi, succibi, harpies, devils, imps, and haunters of Avitchi, from all the teachings of history, sacred and profane, Hindu, Egyptian, Greek, mediaeval, Swedenborg, Rosicrucian, theosophy, theology, with every last ounce of horror, mystery, shivers, and creeps squeezed out of them.  They were gorgeous ghost stories, for they were told by a man fully informed as to all the legendary and gruesome details.  At first I used to think he might have communicated it more effectively.  Then I saw that the cool, drawling manner, the level voice, were in reality the highest art.  He told his stories in a half-amused, detached manner which imposed confidence more readily than any amount of earnest asseveration.  The mere fact of his own belief in what he said came to matter little.  He was the vehicle by which was brought accurate knowledge.  He had read all these things, and now reported them as he had read: each man could decide for himself as to their credibility. 
question: What false assumption did the narrator initially make?
answer: At first the narrator thought that he could have communicated more effectively, but didn't realize the storytelling techniques were the highest art