Originally posted by: Major fatal Moebius

If Luke wins, the Emperor gets a shiny new apprentice.

I don't believe that one bit, actually. There's no reason to believe Luke would ever join the emperor, even if he killed his father, Darth Vader (lol), using the dark side of the force. I'd reckon Luke would rather be killed and tortured by the emperor than join him. Throughout the entire tirlogy there is no indication of Luke descending to the dark side, with perhaps the exception of the philosophic cave meeting that took place in ESB and maybe some of the anti-Obi-wan-ness. If George Lucas wanted us to believe Luke could turn to the dark side, he should have made a better case imo. Still, this is only a very, very minor flaw for me.

Here's my thoughts on it.

Darth Vader was using Lukes thoughts against him to manipulate him into turning to the dark side by giving in to his anger. When he mentions says "you have a twin sister, if you won't turn perhaps she will," that gets to Luke. He goes nuts and gets angry, he is giving in to his anger, making his fail turn. He uses it to make his more powerful, and the result is he ignites his saber and charges vader with anger, knocking him to the ground and cutting off his hand. That's the final turn of Luke. Only when he looks at his fathers robotic wrist stub and then his own robotic hand does he release what he is becoming. His father. By giving into his anger, he is becoming the very person he is trying to save. That's were the emperor had his overconfidence. He didn't see luke stopping like that. Luke showed more inner strength than the emperor thought by reeling himself back in, calming down letting vader live and proclaiming he is a jedi.

I always felt the idea was is he had killed vader in anger, he would be lost and would have turned because he would have fully given in. By stopping just short of it, however, he didn't turn, he showed his inner strength as a jedi. He didn't give in. I think the emperor was so smug because of his overconfidence. That overconfidence is shown by the fact he could not sense the good in vader. Only Luke sensed it. The emperor was so sure of himself, he couldn't sense that little bit left. He was sure Luke would turn with poking and proding. He felt he was like his father in that regard, and once he started the turn he wouldn't stop. Luke, as we know, shoulded him otherwise.