Continuity mistake: When Luke is riding the speeder bike against the trooper, the black glove on his right hand jumps to his left and then back again. (01:01:15)
Other mistake: During the fight between Luke and Darth Vader, when Vader throws his lightsaber at Luke, it is not only Luke's lightsaber from Episodes IV & V instead of his own, it is ignited upside-down, with the blade protruding from the pommel rather than the emitter. (01:50:20)
Revealing mistake: Vader tosses the Emperor and then collapses on some barrels next to the railing. Look at Vader's arm - the one with the severed hand. His arm is bent at the forearm in a way that arms just don't bend. This is because David Prowse's hand was inside an "elongated" arm to simulate it being chopped off. He couldn't keep his wrist straight, giving the appearance of a bent forearm. (01:57:00)
Revealing mistake: When Jabba's sail barge begins to explode, you can see that one of the floating skiffs is standing on stilts. (00:36:30)
Answer: Yoda. When he was departing for Cloud City to save his friends in the previous film, he promised Yoda that he would return to Dagobah to complete his training.
Phaneron ★
OK. But I thought he was talking about the holeish thing in his hand since he covered it up when he said it. I must have misunderstood it.
The hole in Luke's robotic hand reminds him that he got that robotic hand in the first place because he lost his duel with Darth Vader at Cloud City - a confrontation Yoda warned him he was not ready for.
TonyPH