"As you wish."
Westley employs this phrase many times over the course of the story, particularly in the beginning of his relationship with Buttercup, to communicate to her that he loves her without saying it outright. The phrase is a catalyst for the entire plot in this regard, and becomes permanently associated with Westley's identity. While masquerading as the Dread Pirate Roberts, he is therefore able to use the phrase to reveal his true identity to Buttercup. Additionally, at the end of the movie, the grandfather uses the phrase to tell his grandson simultaneously that he'll read him the story tomorrow, and also that he loves him.
"Hello. My name is Inigo Montoya. You killed my father. Prepare to die."
Inigo's character is defined by his 20-year quest for revenge, which he hopes to culminate in the striking down of his father's murderer, after delivering this well-practiced phrase to him. That he says it so many times in the film speaks to how often he's thought about this confrontation and planned out the details of it. At the film's climax, when he succeeds in besting Count Rugen, the phrase becomes like a beacon of strength for him: the more times he says it, the faster he regains his strength and gains the upper hand over his opponent. In this way, the phrase represents his tireless ambition and desire to avenge his father, which he uses as fuel to ultimately take Rugen down. Today, this line is one of the most memorable from the film; most anyone who has seen it can recite it to you, and even those who haven't are at least familiar with it, in part thanks to its use in popular internet memes.
"Inconceivable!"
Like Westley and Inigo, Vizzini boasts a catch phrase which he repeats constantly. In his case, however, he utilizes a sophisticated word like "inconceivable" to mask his obvious incompetence. Vizzini is quickly established as being all talk and no action, screaming at his vastly stronger and more skilled henchmen to try to keep them in line, when in reality he needs their skills to carry out his work. When Westley confronts him, Vizzini boasts at length about his intellect and asserts the utmost confidence in his ability to outwit him. That he ultimately keels over in a hilarious, mid-sentence sudden death proves that he was all talk, and his continued use of a word like "inconceivable" up until that point is a constant reminder of this. In reality his vocabulary isn't enough to save his life.
"This is true love. You think this happens every day?"
The foundation for Westley and Buttercup's connection is that they share "true love." What that is exactly isn't explicitly defined in the film, but we are made to understand from early on that their connection is deep and unyielding, and that they want each other more than anyone or anything else. Establishing their relationship as a rare, genuine, passionate one like this helps the audience root for them as the story progresses, and falls in line with the dramatic elements typical of a swashbuckling adventure tale.
"My Westley will always come for me."
Buttercup spends the majority of the movie assuming the role of damsel-in-distress, and to this end she holds tightly to the promise Westley made that he will always come for her, especially when she's in peril. This belief helps sustain her love for him even after she believes him to be dead and agrees to marry Humperdinck, and even after she bargains for his life and they're separated again. Her unwavering faith in him is a testament to their true love, one of the foundations of the story.
"We'll never survive."
"Nonsense. You're only saying that because no one ever has."
While undoubtedly a funny moment in the script, this line also demonstrates a common dynamic between Buttercup and Westley: by and large, she assumes the role of pessimist and he the role of optimist, particularly throughout the scene with the Fire Swamp. As the quintessential savior, Westley's bravery and skill help him to feel confident in the face of dangerous situations; this is true when he's dueling Inigo, fighting Fezzik, and outsmarting Vizzini. His continued success against difficult odds fuel his ability to think positively. Buttercup, on the other hand, has experienced hardship after hardship and so approaches the Fire Swamp with skepticism and pessimism. Simple interactions like this one serve to remind us of these character traits.
Miracle Max: "Have fun stormin' da castle!"
Valerie: "Think it'll work?"
Miracle Max: "It would take a miracle."
Billy Crystal and Carole Kane's hilarious scene in The Princess Bride is one of the most memorable in the film, and this exchange at the end of the scene is particularly clever. Westley's odds of penetrating the castle and saving Buttercup are astronomically small in his present state (and, of course, without Fezzik and Inigo, would have been nil), for which reason they seek out Max and Valerie to help. Perhaps it would "take a miracle" for them to win the day, but with the help of a miracle worker, things look less grim. Max's quip is therefore simultaneously pessimistic and optimistic; they need a miracle to succeed, but, if he's confident in his abilities, that's exactly what he's given them.
"I want my father back, you son of a bitch!"
This is the climactic moment in which Inigo finally gets revenge on the man who murdered his father. Count Rugen shows cowardice and weakness in his final moments; Inigo demands money, power, all the ordinary goods a person might want, and Rugen submissively concedes to his requests, hoping to be spared. We soon see that Inigo is making a point: there is nothing that Rugen could give him to replace what he took away, and so he must die the way Inigo's father did. This line is not only an affirmation of that, but also a genuinely emotional and dramatic moment in the film, and one of the only moments where the film seems to take itself seriously, choosing not to trivialize the moment with lighthearted humor as in other scenes.
"Well, who says life is fair? Where is that written? Life isn't always fair."
While many loose ends are tied up at the end of the story and all appears well, one of the takeaway messages of The Princess Bride is that life isn't always fair, a notion accurately put forth by the grandfather here when the boy is angry at the possibility of Buttercup marrying Humperdinck. At its heart, The Princess Bride is about stories, and about both the good and bad that they contain, whether or not we want them to; sometimes, we are forced to reckon with an unhappy conclusion. One example of this is Westley's decision to leave Humperdinck alive. Surely, any audience would've been happy to see him die after all the pain and suffering he's caused, but Westley decides to take the moral high ground by leaving him to suffer alone, a decision that we the audience have to accept even if it isn't necessarily "fair." As the boy comes to understand this over the course of the tale, so must we.
"Your Westley is dead. I killed him myself."
"Then why is there fear behind your eyes?"
Even at his most vile, Humperdinck is hard-pressed to intimidate Buttercup; she has known Westley's loss before and allowed it to shatter her. After learning that he is alive and reuniting with him, her faith that he will always come for her is reinvigorated, such that even when Humperdinck tells her outright that he murdered Westley, she rightfully doesn't believe him. Instead, she makes him aware of his own uneasiness, a tactic meant to turn some of his intimidation back onto himself.
