I always liked this line by Luke in ROTJ. I thought it perfectly described the Emperor at that moment thinking he was perfectly safe on the Death Star #2. I was thinking about the PT and there seems to be another moment when Darth Sideous shows his "weakness." This is when Padme/Amidala goes back to Naboo to take the fight to the Trade Federation. Sideous says, "This is an unexpected move for her. It's too aggresive.. Lord Maul, be mindful." It was clear that he didn't forsee her doing what she was doing. This seems to be a good setup for the rest of the movies. It shows his weakness, but also allows a build-up to what happens in ROTJ. From this point on, everything falls into place the way the Emperor expected it to be and leaves him open for the unexpected triumph of the Rebels and Vader's/Anakin's turnaround.