I found this letter matching envelope tucked in a copy of "If This Be Treason" by Margaret Echard. The letter is from Echard, answering a letter from a fan of her writing:
Jan 7 '46
Dear Margaret Johansen,
Thank you for your Christmas greetings and the nice things you said about the books. It is always heart warming to an author to hear from a reader like you. My only other book beside the ones you mention is "Before I Wake." Have you had that one yet? I hope to have a new one out before too long.
I wish I could give you an infallible rule for success in writing. I know but one. If you feel the urge, write and keep on writing. There is no short cut.