What a wonderful thread! Love all the Pratchett, Susan Cooper, P&P, Hitchhikers, Harry Potter & LPW already quoted.
I can't believe no one has quoted any Yeats!
"But one man loved the pilgrim soul in you / And loved the sorrows of your changing face" (When You Are Old)
"I have spread my dreams under your feet / Tread softly, for you tread on my dreams" (He Wishes For the Cloths of Heaven)
"Why, what could she have done, being what she is? / Was there another Troy for her to burn?" (No Second Troy)
And a couple from novels:
"If you were born with the gift, then you must serve it, and nothing in this world or out of it may stand in the way of that service, because that is why you were born and that is the Law." (The Dark is Rising)
"I feel like the word shatter." (The Handmaid's Tale - I know that feeling!)
"I lack the World, for I move like a Ghost through it" (Hawksmoor)