Continuity mistake: When the little Ewok finds Leia, and she rises up, he points his spear at her and you can see that the front of his leather hood is over the spear's shaft. The shot changes to Leia, the back to the Ewok and now spear is over the hood, the shots change again and now the hood's front is crumbled up between the spear and the Ewok´s body.
Visible crew/equipment: The rancor puppeteer's arm can be seen on the far right side of the screen as it starts poking at a hiding Luke. Widescreen version only.
Continuity mistake: Before the Emperor gives permission to fire the Death Star, in the scene at the bridge of the Star Destroyer, the blue rank insignia of Admiral Piett and another Imperial officer is coloured black. This is probably caused by bluescreen effects replacing everything blue with the colour of space. This can also be seen when a Rebel ship hits the Star Destroyer at the end of the film.
Revealing mistake: In many of the scenes taking place in outer space, if you look closely you can see polygon borders surrounding space vehicles (X-Wings, Star Destroyers, and even the Death Star) indicating the objects being superimposed into the outer space background. [This mistake may only apply to the Blu Ray version.]
Revealing mistake: When Luke is in the Rancor pit, there is a Rodian in the crowd - some of his fingers are hanging from his hands. Cheap costume. He makes hand gestures like Mr. Burns - helps to find him.
Deliberate mistake: When Luke is to be executed, Jabba says, "Put him in", and there's a shot of the prisoner's skiff. The shot has been flipped, seen from the positions of Lando and the guards, as well as the railing of the skiff.
Continuity mistake: In one scene of the battle of Endor, Chewbacca is accompanied by 2 Ewoks while pursuing one of the ATSTs. However soon after their first appearance, one of the Ewoks' costume looks completely different from the original one.
Continuity mistake: After the Death Star explodes, Wicket the Ewok comes over to Han and Leia, and Leia puts her hand on his arm, and Han puts his hand on his shoulder. In the next close-up of Wicket, their hands are no longer there. This is best seen in the widescreen version.
Continuity mistake: When Leia frees Han from the carbonite, he falls on the ground and has dirt on his face. Some shots later, the dirt is gone.
Continuity mistake: On the forest moon of Endor, when Chewbacca finds the dead animal, it's attached on a little tree but when they are trapped in the net, the animal is still there, but the tree has disappeared.
Continuity mistake: As we follow Fett's flight after being hit by Han, we cut to a scene showing the front half of a skiff. Luke then kicks one of Jabba's henchman. He very clearly misses the man by a few inches, yet the man still tumbles to his doom nonetheless.
Revealing mistake: After the rebels have destroyed the radar on Endor, there's a shot of Lando and a Sullustean laughing, and after that, a shot of spaceships. One Y-Wing passes in front of an X-Wing, but the light of its engines disappears a little bit before.
Continuity mistake: When Han, Luke and Chewbacca are sentenced to death, there's a strange alien with a long tongue hanging from the ceiling, in the upper, left hand corner. In some shots, the creature is moving, in other shots, it is completely still and appears to be asleep or something.
Other mistake: Look at the shots of the windows in the Emperor's chamber on the Death Star. When they are seen from a distance, the window frames are out of focus, but the stars remain in clear focus.
Continuity mistake: In the scene on Endor where Luke and the Stormtrooper are duelling on the speeder bikes. The glove on Luke's damaged hand changes sides between the front and side on shots.
Revealing mistake: In one quick scene when Luke's hologram is talking to Jabba, the film has been reversed. The camera shows Jabba sucking on his 'bong' and then pans down to Salacious Crumb. However, during the Jabba shot, the air bubbles in the 'bong' are going down, as opposed to surfacing. Behind Jabba, you can see the smoke created is also going downward.
Continuity mistake: At the very end of Palpatine and Vader's conversation, we are tight on the Emperor. He is walking past a series of grey suited officers. But when we instantly cut to a wide angle shot, they are now in front of rows of stormtroopers.
Continuity mistake: This is a 'Special Edition' error only. After the scene in Jabba's palace when R2D2 and C3P0 are assigned their 'duties' we see the audience chamber in their party, and Jabba holding his dancing girl's leash. When the first song ends, Jabba says 'Do that again' and his hands are empty. When next he's shown, the leash is back in his hands.
Continuity mistake: The stormtrooper that is chasing Leia on the forest moon of Endor has a symbol looking like IZ on his helmet. It keeps disappearing during the scene.
Continuity mistake: When Yoda is lying in bed, the creases in the blanket over him keep changing between shots.
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