All credit to Madeleine L'Engle

"If we knew ahead of time what was going to happen we'd be--we'd be like the people on Camazotz, with no lives of our own, with everything all planned and done for us. How can I explain it to you? Oh, I know. In your language you have a form of poetry called the sonnet." ....
"Yes."
"There are fourteen lines, I believe, all in iambic pentameter. That's a very strict rhythm or meter, yes?"
"Yes." Calvin nodded.
"And each line has to end with a rigid rhyme pattern. And if the poet does not do it exactly this way, it is not a sonnet, is it?"
"No."
"But within this strict form the poet has complete freedom to say whatever he wants, doesn't he?" ....
"So what?"
"Oh, do not be stupid, boy!" Mrs. Whatsit scolded. "You know perfectly well what I'm driving at!"
"You mean you're comparing our lives to a sonnet? A strict form, but freedom within it?"
"Yes." Mrs. Whatsit said. "You're given the form, but you have to write the sonnet yourself. What you say is completely up to you."

"Do you think things always have an explanation?"
"Yes. I believe that they do. But I think that with our human limitations we're not always able to understand the explanations. But you see, Meg, just because we don't understand doesn't mean that the explanation doesn't exist."
"I like to understand things," Meg said.
"We all do. But it isn't always possible."

(from "A Wrinkle in Time")