JK Rowling famously wrote, “I open at the close.”
Stephenie Meyer wrote the rough draft of Breaking Dawn before writing New Moon or Eclipse.
Stephen King writes about being surprised by his characters and their decisions in his book, On Writing.
Mary DeMuth says, “It’s both/and. I know the basic ending, but I don’t know how I’ll get there. There are surprises all along the way.” (I asked on her Facebook page.)
Do you write as if you were following a map to the X? You know the final destination.
Do you write as if you were the passenger just along for the ride? You are surprised by where your writing takes you.