Jane learned not to trust people from Mr. Brocklehurst.
Jane already had trust issues because of had badly she was mistreated by her aunt. Mr. Brocklehurst demonstrated to her that adults often mistreat children. His school was so poorly run that children dying was a fairly common occurrence.
Consider his reaction when young Jane tells him that psalms are not interesting.
“That proves you have a wicked heart; and you must pray to God to change it; to give you a new and clean one: to take away your heart of stone and give you a heart of flesh.” (ch 9, p. 25)
He took Mrs. Reed’s word for it that Jane was a liar, and never gave her the benefit of the doubt. He was, in short, a terrible schoolmaster and guardian. His religious ideas were all fire and brimstone, and he had no appreciation for individuality.