Writing a novel in a month is a dream. Breaking it into pieces and writing a little each day makes it attainable. However, when you've already written 20,000 words and come up with a fantastic idea you wish you'd had earlier--it's time to add the idea and weave threads back into the 20,000 words so the newly formed idea makes sense.
Take and exisiting scene and expand it. Word backwords and weave threads of logic to make the new detail work.
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NaNoWriMo Current Word Count: 26,890