quotes from The Phantom Tollbooth

"I'm not very good at problems," admitted Milo.
"What a shame," sighed the Dodecahedron. "They are so very useful. Why, did you know that if a beaver two feet long with a tail a foot and a half long can build a dam twelve feet high and six feet wide in two days, all you would need to build the Boulder Dam is a beaver sixty-eight feet long with a fifty-one foot tail?"
"Where would you find a beaver that big?" grumbled the Humbug as his pencil snapped.
"I'm sure I don't know," he replied, "but if you did, you'd certainly know what to do with him."
(175).

"Yes, indeed," they repeated together, "but if we'd told you, 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."
(247).

"But that can never be," said Milo, jumping to his feet.
"Don't be so sure," said the child patiently, "for one of the nicest things about mathematics, or anything else you might care to learn, is that many of the things which can never be, often are. You see," he went on, "it's very much like your trying to reach infinity. You know it's there, but you just don't know where--but just because you can never reach it doesn't mean that it's not worth looking for."
(197).