The Empire Strikes Back (1980) is the third film in the Star Wars saga, following on from Star Wars (1977) and The Star Wars Holiday Special (1978). The Empire Strikes Back is sometimes considered to be "the one where the Empire wins" by foolish mannys on the internets. All cats know that the Empire does not win, for the following reasons.
Darth Vader and the Evil Emperor's main objective in The Empire Strikes Back is to capture Luke Skywalker so they can turn him to the Dark Side of the Force, or else kill him if he will not do that.
"He will join us or die, my master."says Darth Vader.
After the rebels escape him at Hoth, Darth Vader concocts a plan to catch Luke by first capturing Han Solo and Princess Leia and using them as the bait in a trap for Luke. This works perfectly and Luke is indeed lured to Cloud City before completing his Jedi training with Yoda.
However, at this point Darth Vader's plan goes wrong and, at the end of the film, Luke is neither captured nor killed. His plan goes wrong in two important ways.
Firstly, in the most famous scene in all of Star Wars and one of the most famous scenes in all films ever made by mannys, Darth Vader fails to persuade Luke to join him and Luke instead chooses to fall down to escape him. Darth may have had the upper hand throughout their lightsabre fight, but he underestimated Luke here just as when he failed to freeze him in carbonite earlier because of Luke's cat-like jump.
Perhaps Luke was jumping to his death (he doesn't exactly land on his feet like a cat would have done after that fall), which would have qualified for the "or die" part of the plan, except for the second way in which Darth Vader's plan goes wrong.
Luke is saved by Princess Leia and Lando in the Millennium Falcon, and they are only free and on the rebels' side respectively because Darth Vader made a mistake. Lando didn't like working for Darth Vader but he had no choice and was too cowardly and self-interested to do anything about it.
But then when Darth altered the deal with Lando he pushed Lando too far and Lando acted to redeem himself when he rescued Princess Leia, Chewbacca and C3P0. This meant they were free to save Luke in turn.
Darth Vader is left empty-handed and The Empire Strikes Back ends not with the Empire winning but with Darth Vader coming out as the biggest loser of all.