One of the scenes that has taken me for forever to understand exactly what is going in Star Wars was Luke's Dark side vision in the cave on Dagobah in the Empire Strikes Back. The confusion starts while Yoda and Luke are talking about the dark side just before they arrive at the cave, it seems like kind of a random conversation, but Yoda is actually telling Luke how to pass the cave test. He tells Luke that a Jedi uses the force for self-defense only, never for attack. So in the cave Vader attacks Luke and after a few parries Luke decapitates Vader, which I thought was OK since it was in self-defense, as Vader attacked first. Then later when Luke was leaving Dagobah, Yoda tells Luke yes remember your failure at the cave. So what failure was Yoda referring too? I mean Luke won in self defense, how was that a failure? It wasn't until something Rey said in the Last Jedi about her cave vision, that finally helped me understand what happened in Luke's. Rey said, I thought that there was something for me there but there wasn't. The dark side tempted her with knowledge of her parents and she refused to touch the dark side. But in Luke's case the Dark side offered Luke the power to beat Darth Vader, and Luke took it. They should have a little caption in the movie "Luke uses the Dark side". The cave test is a test to see if a Jedi can resist the temptation to use the Dark side and Luke failed. I think that the mask coming off and Luke seeing his face might also be an indication that Vader is of Luke's blood, while also foreboding that if Luke continues to touch the Dark side he will end up like Vader. When you take this into account while Luke is leaving Dagobah, that he has failed to resist the Dark side and that Luke has made the same decision his father did when he chooses the love of his friends over his duty as Jedi. You can really feel the weight of the darkness that the Jedi are facing in that moment, the outlook for Yoda and Obi-wan at this moment is very bleak. Viewer Note: When watching all the Star Wars Films in order, do not, do not watch Rogue One with in like six months of watching Empire Strike's Back, it makes Empire's Hoth scene look bad, and brings up all kinds of questions that don't have good answers. Enjoy!!