What a great letter! I haven't had the experience with proofreaders, or editors, or sales. But I imagine my responses would be close to what Steinbeck's are; my books are my babies in a sense, and I'm never ready for them to go out into the world. I felt the same way about papers I had to write in college - they never met my expectations and always needed more editing. There comes a point where writers have to declare the product finished and let it go, otherwise it would never be finished!
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Well-behaved women rarely make history. - Laurel Thatcher Ulrich
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