The Non-Canon Expert explains Darth Plagueis’s reasons for finding contempt with the methods and practices of the ancient Sith, slowly causing him to lose respect for them and engage in a new path forward in achieving the long awaited Sith Grand Plan.
This is a Legends story for Darth Plagueis and the ancient Sith with information primarily found within the novel «Darth Plagueis» by James Luceno and works such as the Book of Sith. I hope that you enjoy it!