"Do you always write the ending first?"
No, because the exact *shape* of the ending never come clear to me until
after I've written all the material preceding. I *know* where it's going,
I have a fairly clear vision whenever I write a script of where I want it
to end, but I don't actually write it first, no. Mark Twain said, "You
should never write a story until you have finished it to your
satisfaction." So yeah, you do have to know it.
jms