Fred's first impressions of Sophia were that of joy and excitement, but it is through these strong feelings for her at first that he transforms his compassion for her to absolute hatred. It is tough to see a person who you had faith in at one time, turn in to a person who at times chooses to disregard you as a human being. Slavery transformed Sophia from a "warm, and tender-hearted woman" into a person whose character resembled that of a "tiger-like" fierceness. Slavery brought out the wickedness in Sophia's soul, which in turn demonstrated the dehumanizing aspect of slavery on her. The tone in which Douglass speaks gives the reader a sense of how sincere he thought Sophia to be, but as time progressed Fred soon saw the "fierceness" in her eyes, and that is what hurt him so much. Slavery was a new concept for Sophia, and it is because slavery was new to her, that she reacted the way she did when her husband yelled at her about teaching Fred to read.
Sophia went from teaching Fredrick the ABC's, to receiving pleasure by ripping the newspaper out of his hands. Instead of being rational with Fred, after the incidents with Mr. Auld, she turned into a person whose personality took a 360-degree turn. It is this change in Sophia's nature that hits Fredrick where it hurts the most. "Slavery proved as injurious to her as it did to me." Fred comments on how slavery has dehumanized her, for he realizes that it was because of slavery, that Sophia became who she was. It saddens both Sophia, though she may not choose to recognize it, and Fredick, to see a person of such kindness, turn into one with no thoughtfulness.