I've got another theory...
When someone is successful for a long period of time, they start believing that they are invincible and that their way is the only way.
The number of people willing, or brave enough to say, "No...you're wrong" dwindles, and it becomes increasingly difficult for the person to gain perspective.
...and "We are a grandmother" led quite a lot of people to believe that she'd lost, if not all, then at least a significant amount of her allotted marbles.