Lady Rockabella no longer wanted to use methods such as slapping and smothering to punish. She wanted to find a better and more effective method of doing it so she settled on ball torture after she had done some research. The mistress even bought some torture tools which she would use in her mission and the mistress was sure that success in what she intended to do was virtually guaranteed.
Lady Rockabella does not like shallow minded people and this guy seemed to be one of those who were shallow. She had to make him aspire for more and better and so she used her ballbusting to dominate and torture him. The pain he felt enabled him to change the way the mistress wanted him to. And after that, he did not take pride in his shallowness and he tried to change.