My favorite from The Chronicles:
Puddleglum, having stuck his hand in the fire to gain a moment of clarity from the spell binding words of the Queen of the Underland:
“Suppose we have only dreamed, or made up, all those things—trees, and grass and sun and moon and stars and Aslan himself. Suppose we have, then all I can say is that, in that case, the made-up things seem a good deal more important than the real ones...four babies playing a game can make up a play-world which licks your real world hollow. That’s why I’m going to stand by the play-world. I’m on Aslan’s side even if there isn’t any Aslan to lead it.”
This theme seems prevalent. Here's the flip-side, in the Screwtape Letters, Wormwood is advised to sidetrack his client after he leaves his books: "Your business is to fix his attention on the stream. Teach him to call it "real life" and don't let him ask what he means by "real". Remind him real life, a newsboy, a bus.
The further...in you go, the bigger everything gets. The inside is larger than the outside. ~ C. S. Lewis, The Last Battle