Answer: Discovery
The short story begins with a sorrowful tone but soon evolves as the narrator/author discovers that he could rearrange the scene in front of him.
"What was it—I paused to think—what was it that so unnerved me in the contemplation of the House of Usher?" Narrator begins to think why he feels unerved by the house.
"I was forced to fall back upon the unsatisfactory conclusion, that while, beyond doubt, there are combinations of very simple natural objects which have the power of thus affecting us, still the analysis of this power lies among considerations beyond our depth." Narrator begins to discover that there is something beyond his depth.