Metaphor

metaphor: a figure of speech using an implied comparison of seemingly unlike things or the substitution of one for the other, suggesting some similarity

"O'Brien smiled slightly. 'You are a flaw in the pattern, Winston. You are a stain that must be wiped out."
                                                                                                         -1984
                                                                                                  by George Orwell

Here O'Brien compares Winston to a stain.Stains are unwanted and ugly things, many times ruining an article of clothing. Stains are imperfections. O'Brien is saying that Winston, who thinks for himself and tries to reason is an imperfection in the cloth of mindless followers. Orwell uses this metaphor to preach about what the future of the world looks like to him. He is trying to communicate that anyone who has any individuality whatsoever will be annihilated. He is attempting to hang a sign that reads "Turn Back Now, Danger and Misery Ahead" for the world to see by showing them that the aspects of life which allow pleasure and friendships to form will be completely gone in his predicted future.