In Star Wars: The Empire Strikes Back, Luke goes to Dagobah to receive training from Yoda, a Jedi Master. As the training progresses, Luke sees his X-Wing sink deeper into the swamp where it landed. Yoda tells him to use the force to get it out of there. He tries, but manages to levitate it only slightly.
When he gives up and sits on the bank, Yoda is able to get the fighter out of the swamp and onto dry land using only his mind. Luke is so surprised he did it, he states that he cannot believe it. To which Yoda replies, “That is why you fail.”