There's something not right here. I feel cold, death (Luke Skywalker)

Wie geht's?

The dark side within (a chapter of The Dharma of Star Wars by Matthew Bortolin) has an interesting take on that scene in Empire Strikes Back that I've often puzzled over.

After a Yoda training session Luke looks into a creepy dark cave. Yoda tells him it's 'a domain of evil' and that Luke must go into it!

Whaaat? But Luke is a curious young guy and so he ignores Yoda's advice about taking a weapon and in he goes.

Everyone knows what happens next in the cave - Darth Vader 'appears', they battle and Luke 'wins' only for the Vader mask to disappear and reveal Luke's own face!!

Whaaat???

This is deep stuff. Wot's uh the deal?

Well the deal is, that Luke has to confront the dark side in that cave. 

As Matthew explains:

The dark side is all the suffering in life: it is frustration, hatred, anger, and all the negative feelings and thoughts that come from within us. By going into the cave Luke is penetrating his own nature on a quest to recognise himself and the source of his difficulties. Yoda knows that if Luke can confront what lies within with courage and compassion, he will do much to overcome whatever hold the dark side has on him. But Luke makes the same error many of us make in our lives: he mistakenly believes his suffering comes from somewhere outside of himself. In this case, Darth Vader is the apparent source.

Love and peace - Adson Purwa (Jedi master)