The message that some parents send to their children is that their value is based upon what they accomplish, and is not intrinsic. To me Spears seems like someone whose total sense of self-worth is based upon her achievements, and that she does not have a well-developed sense of self and self-worth. That's a very fragile self-concept, and when her stardom started to wane her sense of who she is in the world may have become very unclear to her.