Crazy ran in the family, but it was very well hidden when Rochester was wooing Bertha. Rochester became friends with Richard Mason, met Richard's sister Bertha and fell in love (she was beautiful, demure, quiet, yielding. You know, "all that is feminine.") The Mason family did a VERY good job of hiding Berta's brand of crazy and made sure that Rochester didn't spend too much time alone with their darling, "virtuous" child; all very good ways to keep Rochester from realizing that Bertha was batshit insane under that pretty exterior.