Why Did Palpatine Lose To Darth Vader?

How did Emperor Palpatine lose to Darth Vader. The Sith Lord who meticulously planned his rise to power and the corruption of Anakin Skywalker to the Dark Side for decades?  Palpatine was blindsided by Darth Vader and thrown to his death while he was attempting to kill Luke Skywalker in Return of the Jedi. But was Palpatine really blindsided? Maybe he had foreseen Vader's betrayal and planned for it. Maybe Palpatine knew he couldn't win against Luke Skywalker and bided his time until the Last great Jedi perished, leaving the Galaxy to be retaken now that there were no Skywalkers to interfere with his plans. We'll attempt to find out in this episode of Star Wars Theory.