That initial urge to show your work to people ASAP is only natural. Until other people absorb your stuff into their brains, it's in a vacuum. Might as well not exist. If a script sits on a hard-drive with no-one around to read it, does it make a difference? No. Only to you, at this point in time, unless you have an agent who's badgering you to finish it, or at least waiting for it.
Hand in hand with that drive to show people, comes the feeling that whatever you write in that vast, gaping, intimidatingly blank Final Draft file will be read. Sometimes, that feeling can bring about a terrible paralysis. You're standing on the brink of a huge vortex of possibility. Worst of all, there's the sense that This Is It. No more talking: it's time to do. Time to prove yourself to the world. Again.
Me, I love the first draft. Love that open road, beckoning you to burn rubber. Most of all, though, I love the fact that no-one will ever read it.
This is because the first draft you hand to Important People should never be the actual first draft, but crucially, the first draft you've decided to show them. Personal first-draft, public first-draft. Very different beasts.
For another thing, the concept of Draft Zero helps cement the idea in your head that this draft is your own personal sandpit. Sure, you're taking it seriously and making every effort to construct a strong skeletal structure to which you'll eventually graft muscle, organs and finally beautifully flawless skin, Hellraiser-style. But at the same time, you have absolute carte blanche to fuck it up. You can't win unless you're not afraid to lose. Forget all external pressure and fuel yourself with internal pressure: the burning desire to write this story before you die of anticip-p-p-pation.
Launch yourself into that sandpit and write like the seven winds. Momentum is everything. Never look back. Pretend you're being chased by a shark which devours words (an image which reminds me to strongly recommend Steven Hall's extraordinarily vivid and imaginative novel The Raw Shark Texts). Some writers continually stop, survey what they've written, then go back to fix it. If that method works for them, great, but I can't do that. Momentum, momentum, momentum. When I realise I've messed up, or that things will need to be fixed later, I make Running Notes, then just keep writing.
When you reach the end of that fun, breathless marathon, what you have is Draft Zero. And it's yours. All yours. A template for future greatness.
You'll go back to rewrite it again and again, restructuring, ironing out the many flaws, de-clunking that often laughable dialogue, starting to introduce or strengthen those lurking themes. And at the end of that process, that's when you emerge triumphant from your steaming, churning brain-factory with The Actual First Draft.
Draft Zero is your own personal, very private firstborn. Enjoy the vacuum in which it resides. In space, no-one can hear you scream that it hasn't turned out quite how you expected.