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.
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.
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.
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.
Continuity mistake: When the droids enter Jabba's throne room, a three-legged R2-D2 rolls out on the floor. In the next shot, the droid no longer has his third leg deployed.
Continuity mistake: After Luke leaps up to the catwalk during the lightsaber duel, Vader's left shoulder is more covered by his cloak than in the previous shot of him.
Continuity mistake: In the Emperor's throne room, the existence and arrangement of several of the canisters on each side of the lift/elevator changes between shots, several times.
Continuity mistake: During the final battle, when some moving ships explode, the fire and the debris suddenly stay stationary.
Continuity mistake: When Leia frees Han from the carbonite, the light shining on the walls and floor keeps changing. For example, watch the light on the right side of the carbonite block.
Continuity mistake: When Chewbacca gives Han a hug in his prison cell in Jabba's palace, he initially puts one arm around him, but as the shot changes both Chewbacca's arms are around Han.
Continuity mistake: When Luke throws a scout trooper off of a speeder bike on Endor, the trooper mysteriously hits a tree back first, but he should have hit the tree face-first. He only rotated across his horizontal axis.
Continuity mistake: After the Ewok takes off on the speeder bike, Han says, "You stay here, we'll take care of this." Leia turns and she can be seen with a very large smile, even showing her teeth. When the camera instantly cuts to a different angle of the scene, Leia is no longer smiling, displaying a deadpan look.
Continuity mistake: In the fight scenes on the skiffs with Jabba the Hutt's men, the skiff that Han and Chewie are on is hit with a laser blast and Han falls over the edge feet first, yet in the following scene he is hanging upside down with Chewie holding his feet.
Continuity mistake: In the lightsaber duel between Luke and Darth Vader, Luke chops off Vader's hand twice before Vader falls down. The first shot shows Luke's lightsaber striking Vader's wrist, and Vader's hand separating from the wrist. The second shot is from behind and shows the lightsaber chopping Vader's hand clean off his wrist, then it sparks.
Continuity mistake: When R2-D2 is tied up in the Ewok village, the rope that binds him keeps changing position.
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