I’m reading The Phantom Tollbooth with my son, and we came across this gem:

As the cheering continued, Rhyme leaned forward and touched Milo gently on the arm.

“They’re shouting for you,” she said with a smile.

“But I could never have done it,” he objected, “without everyone else’s help.”

“That may be true,” said Reason gravely, “but you had the courage to try; and what you can do is often simply a matter of what you will do.” 

“That’s why,” said Azaz, “there was one very important thing about your quest that we couldn’t discuss until you returned.”

“I remember,” Milo said eagerly. “Tell me now.”

“It was impossible,” said the king, looking at the Mathemagician.

“Completely impossible,” said the Mathemagician looking at the king.

“Do you mean–” stammered the bug, who suddenly felt a bit faint.

“Yes indeed,” they repeated together; “but if we’d told you then, you might not have gone–and, as you’ve discovered, so many things are possible just as long as you don’t know they’re impossible.”

And for the remainder of the ride, Milo didn’t utter a sound. 

pg. 247