There's a passage that I love near the end of Madeleine L'Engle's "A Wrinkle in Time" (1962) that mentions exactly this idea in the context of a discussion on p

There's a passage that I love near the end of Madeleine L'Engle's "A Wrinkle in Time" (1962) that mentions exactly this idea in the context of a discussion on predestination vs. free will, and not knowing what the future holds. "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?" "Yes." Calvin nodded again. "So," Mrs. Whatsit said. "So what?" "Oh, do not be stupid boy!" Mrs. Whatsit scolded. "You know perfectly well what I am 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."