I define writer's block as uncertainty. With every book, there's a question on which direction to go, which characters to follow, what to put in, & what to leave out. To get the book written, these decisions have to be made & sometimes they can block a writer entirely. Having written 18 books now, I have confidence that I can fix any mistakes in the rewrite & that's what new writers have to remember. There will, nay MUST, be a rewrite. Few writers get it right the first time. So make the decision to plow ahead. The magic will come out in the rewrite, at least it does for me. It also helps to have a contract with a deadline. Like a hanging, deadlines tend to focus the mind!