In Chapt 5, in response to Mrs. Weston's assertion that Emma intended see Harriet "better informed" through reading more, Mr. Knightly suggests that since Emma was 12 yrs old "she has been meaning to read more", that she has drawn up a great many reading lists but that she consistently fails to follow through because she lacks the industry and patience.
Chap 9 confirms this insight and tells us that Emma's " views of improving her little friend's mind, by a great of useful reading. . .had never yet lead to more than a few first chapters."
Mr. Knightley seems to have the most clear eyed view of Emma's personality.