For context, Puddleglum the Marshwiggle, along with 2 children and a prince, is trapped in an underground world by an evil witch. The witch uses her powers to try to persuade her captives to forget the world above, telling them that their idea of a sun simply stems from seeing lamps and wishing for a bigger better lamp, and their idea of a lion stems from seeing cats and wishing for a bigger and better cat. After a few moments, Puddleglum answers:

"'One word, Ma'am,' he said... 'One word. All you've been saying is quite right, I shouldn't wonder. I'm a chap who always liked to know the worst and then put the best face I can on it. So I won't deny any of what you said. But there's one thing more to be said, even so. Suppose we have only dreamed, or made up, all those things--trees and grass and sun and moon and stars and Aslan himself. Supose 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. Suppose this black pit of a kingdom of yours is the only world. Well, it strikes me as a pretty poor one. And that's a funny thing, when you come to think of it. We're just babies making up a game, if you're right. But four babies playing a game can make 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. I'm going to live as like a Narnian as I can even if there isn't any Narnia. So, thanking you kindly for our supper, if these two gentlemen and the young lady are ready, we're leaving your court at once and setting out in the dark to spend our lives looking for Overland. Not that our lives will be very long, I should think; but that's small loss if the world's as dull a place as you say."