Trivia: When filming ROTJ, Lucas didn't want anyone to find out that they were shooting the third Star Wars movie, because pandemonium could break out. So when someone asked the crew what they were filming, they said "Blue Harvest". All of the crew had shirts and hats that said Blue Harvest on them. The fictitious film's tagline was "Horror beyond imagination."
Trivia: When they were filming the scenes on Endor, Peter Mayhew was told to stay close to the set so no one would mistake him for Big Foot and attempt to shoot him.
Trivia: When Oola the dancing girl (with those two things growing out of the back of her head) is trying to get away from Jabba, she briefly falls out of the top of her costume. It isn't as visible in the letterbox version, but quite visible in the regular version.
Trivia: The 2 four-note horn blasts (short-short-short-long, call-and-reply) used by the Ewoks to signal their attack to rescue Han and the rebels from the imperials on Endor is the same clarion call used by the Hebrews to signal their exit from Egypt in "The Ten Commandments".
Trivia: The funeral pyre scene wasn't in the original script.
Trivia: There was a rumour that the Lucas crew ran out of space ships in the final battle and threw a sneaker in and used it as a space ship. In the final battle, there is a space ship that looks exactly like the sole of the sneaker.
Trivia: In the new box set of the three original films, they have changed the ending in RotJ to correspond better with the ending in Revenge of the Sith. When Luke sees his father as the Anakin Skywalker spirit, in the final scene at the celebration, it is young Hayden Christensen as Anakin's spirit instead of older Sebastian Shaw, who is the spirit in the original version.
Trivia: Notice when Luke is hiding in the shadows from Darth Vader his face is half shadowed, to represent the decision Luke has to make: one side is light, on the other, dark.
Trivia: This film and the first film (New Hope) were released on the same day, exactly six years apart.
Trivia: In frame by frames views of the scene where Vader lifts the Emperor and throws him down the shaft you can see x-rays of Darth Vader.
Trivia: The alien language spoken by Lando's co-pilot on the Falcon contains elements of Kenyan, and one line literally translates as, "A thousand herds of elephants are standing on my foot."
Trivia: When George Lucas first wrote Star Wars, he was going to have Wookies in Endor but he thought that the movie was going to be so unpopular the he would never release "Return Of The Jedi," so he put Chewbacca in "Star Wars" and the Ewoks in "Return of the Jedi."
Trivia: Ken Ralston, the man who was pretty much in charge of the space battle, put a number of interesting objects in the background. He sometimes used a wad of gum as a far-away shot of a Mon Cal star cruiser, and there is also a sneaker and a yogurt cup floating around.
Trivia: Harrison Ford wanted Han Solo to have a heroic death as he insisted in the first film, but George Lucas didn't agree.
Trivia: There is a shot of a hangar filled with TIE Fighters, and a brigade of Stormtroopers. One of them has a smiley face on his white helmet.
Answer: Darth: "Obi-Wan once thought as you do. You don't know the power of the dark side. I must obey my master." It's implied that the dark side is intoxicating, once you totally give in to the dark side it has a hold on you, and appeals to morality and rationalization are useless against your lust for its power. (On a symbolic level, the dark side is a metaphor for vice. Darth Vader is an addict and abusive parent. It's actually funny how many scenes still make sense if you replace "the dark side" with "the bottle" or similar).
TonyPH
If we bring the prequels into it, it's one of the criticisms of those films that they only make the question of how much Anakin is a "true believer" more confusing. But it stands to reason that at first Anakin may feel vindicated in his resentment toward the Jedi. Later on, Vader may not feel that as strongly, but by then his anger has turned toward himself for failing to save Padme. He may feel that a man as terrible as he does not deserve to be "rescued" from the dark side, leading to a feedback loop where he only gets further enamored with its power and does more evil things which causes him to hate himself even more, and so it goes.
TonyPH