I’ll admit I never write the end first. I need to write chronologically, because I need to expereince the evolution of the story. But I do start writing only if I had an idea of the ending. An idea of the beginning, the climax and the end. Then I know I have a story and even if the plot point will change skin as I write (they almost always do), having that direction, knowing where I start and where I’m heading, like you say, drives my writing process.
Once I could start a story knowin only the beginning. No more. But I have to say that since I started working out the end before startingto write, I’ve always finished all my drafts ;-)