"How do the stems connect to the roots?' 'Where is the mist coming from?' 'Why does one tree seem darker than another?' These questions are implicitly asked and answered in the process of sketching."

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I certainly don't sit down and plan a book out before I write it. There's a phrase I use called "The Valley Full of Clouds." Writing a novel is as if you are going off on a journey across a valley. The valley is full of mist, but you can see the top of a tree here and the top of another tree over there. And with any luck you can see the other side of the valley. But you cannot see down into the mist. Nevertheless, you head for the first tree.

— Terry Pratchett