that poor Mary, being the youngest, was given the least attention. As is seen with modern family dynamics, the child who craves attention will seek it in negative ways if positive attempts are ignored.

Mary's father always inclined his attentions to society and Elizabeth...the pretty one.

Lady Russell's attentions were aimed in Anne's direction.

Mary...well, no one in a parental role much cared for her. She was never considered pretty. I believe the book states that she was never allowed to be more than "a fine girl."

Her way of achieving the spotlight was to be constantly complaining of illness. This habit, probably established in her late childhood after their mother died, continued as her modus operandi into adulthood.

Her dependence on Anne (the only member of her family who paid her any respect or attention or affection) is also the product of this.