Luke's Failure in the cave

Luke's failure is that despite Yoda's insistence that "Your weapons. You will not need them.", he took them anyway, fulfilling Yoda's earlier statement (in response to Luke asking what was inside the cave) "Only what you take with you.".

Some see the Vader in the cave revealed to be Luke as a hint of Luke's parentage, but I see it more as Luke's true enemy is himself (his anger and fear).

His twin failures were reacting fearfully, and resorting to violence.

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I think Luke's failure is that he saw Vader in the first place, and then that he saw himself in the mask. Whatever he saw revealed the fear in his mind

Yoda telling Luke that he didn't need weapons was strange, because JEDI use lightsabers all that time, and going into battle against the SITH without a weapon is stupid. I'm not sure what that was about...

But, when I watch the fight scene, it looks like Luke is very angry, and probably filled with hate, because Vader "Killed" his Father, and he let those feelings control his actions, to win the fight...

Yoda and Obi-Wan keep telling Luke that those things lead to the Dark Side, and that Luke should mind his feelings. Luke was also told he should be fighting with knowledge and skills, for Defense... Not Attack.

When Vader's Mask showed Luke's face, I think that was to tell Luke that his actions were that of someone going to the Dark Side, and that he failed. Just like his father.

Luke was supposed to look "within" when confronted by his fear, and the object of his emotions. But instead, Luke went right for his weapon, struck out in anger and killed the spectre, only to then see its face as his own looking back at him. A vision that not only foreshadows Luke's parentage, but quotes that old Jedi proverb: "he who lives by the lightsaber shall perish by the lightsaber."

It's not only that he brought his weapons, a jedi is allowed to defend himself, but the important thing a lot of people won't notice is that he was the first to draw his sword and thus he is the attacker. Same thing again when he confronts Vader. He has no patience, hastes into battle and thus loses both times.

See, the problem with the failure in the cave is that Yoda goes against everything he says time and time again in the prequel trilogy vs. Empire Strikes Back and Return of the Jedi.