looking at the dialogue of Obi-Wan it looks like Anakin didn't know what the prophecy was or didn't know what being the chosen one is...I guess Obi-Wan said something like that to him
Anakin: Master I heard Qui-Gon saying I'm the chosen one? What does that mean?
Obi-Wan: The chosen one to clean the toilets! Now clean them and I'll maybe get you a new He-Man action figure.
Anakin: Yippieee!
(Hayden said he was more a He-Man fan in his youth than a SW fan)
So I guess that's why Anakin turned...He was tired of cleaning all the toilets of the Jedi, cause as a Sith he only had one toilet to clean, the one of palp (or a bedpan)
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"The greatest hero is the one who learns to face his fears and overconquers it!"
Obi-Wan dives into a forward roll that ends up with him on the rim of a low cliff, just above the soft black sand of a lava riverbank.
Anakin snarls at Obi-Wan, realising he has been tricked. He leaps off his droid at Obi-Wan's back but is half a second too slow.
Obi-Wan whirls to parry Anakin, but his saber doesn't meet Anakin's blade. Instead, he slices off Anakin's leg at the knee. Then he slices of the other leg at the knee. And while Anakin is still in the air, Obi-Wan uses his blade to slice off Anakin's left arm above the elbow. He steps back as Anakin falls.
Anakin drops his lightsaber, clawing at the edge of the cliff with his mechanical hand, but his grip becomes too powerful for the lava bank and the edge crumbles, and he slides down onto the black sand.
His severed legs and his severed arm rolls into the lava below him and immediately burns.
Anakin claws at the soft black sand, but his struggling only makes him slip farther. The sand itself is hot; digging his mechanical arm into it burns off his glove, and his robes begin to smolder.
Obi-Wan picks up Anakin's lightsaber. He lifts his own as well and weighs them in his hands. Anakin had based his design upon Obi-Wan's and thus they appear very similar.
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It comes through compassion, not greed. Love is the answer to the darkness.
SHU MAI
We were promised a reward...a handsome reward!
VADER
I am your reward. You don't find me handsome?
....I'm a little skeptical about that Vader line, but it's so great for another character. I think at this point in the film, it isn't Vader's style to be sarcastic. I'm thinking because he's at this age and is in a mode of being with the Sith and already feeling as though he is the most powerful being in the universe, he can say whatever he wants? This gives a slight bit of hope though, seems like Lucas' writing. I wonder...Ha, it'll be interesting to see how Hayden pulls this line off. If it is even truly a line from the film(which I doubt, but hope for).
After reading Obi-Wan's "You were the chosen one!" dialogue again, it sounds like he could be shouting it after Anakin's already gone in and Obi thinks he's dead. I could see him saying "You were the chosen one!" and "You were my brother, Anakin," in the past tense during the duel. He might just be implying that he doesn't feel that way anymore. But the "I couldn't save you," throws me. That doesn't sound like Anakin is still around.
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I think Obi-wan means he couldn't save you from becoming a Sith Lord, but the line would still make sense before or after the duel, but I agree that it's probably after the fact, more to himself than Anakin.
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'Jedi are at their best when things don't go as planned.' - Anakin Skywalker, whom we now know never met Andro Fenris.