Seriously, this is something which has always bothered me since I was a child.

After saving Han, Luke goes to Dagobah to complete his training, but Yoda says him he already knows everything he needs, BUT... in order to become a Jedi, he must face Vader. Why? Why does he specifically has to face Vader to prove worthy of the title? What does it have to do with the training? I guess he symbolically needs to face his fears, but what about the Emperor? Didn't Obi-wan and Yoda want to train Luke to defeat the Emperor? Will facing Vader make him somehow ready to face the Emperor's knowledge of the darkside?

He then meets Obi-wan, and he says that Luke must face Vader because it is his "destiny" (ha, how convenient! Every now and then, someone says Luke must do this or that because it's his "destiny". How do they know what's his destiny, anyway? :D).

On Endor, Luke decides to leave his "party" and tells Leia he has to meet Vader to "save" him (and also hide their presence to the Empire). He finally meets Vader, but he refuses to come with him. Instead, he decides to bring him to the Emperor (nice work, Luke!)

Face to face with the Emperor (who puts Luke's lightsaber right off his nose), Luke doesn't try to kill him. Why? He's the Supreme Commander of the Imperial fleet which threatens to destroy the Rebels, but he won't move a finger, even when their secret plan seems to be futile.

In anger, he tastes the darkside and tries to kill the Emperor, but is forced to defeat Vader first (which he does), while refusing to submit to the darkside. One more to go: the Emperor. What does our hero do? He throws away his lightsaber and nearly gets killed. What!?

So, what do you think? What was Luke's entire plan all along? :D