When I was in my teens and early twenties there always seemed to be several New Year's Eve parties going on. You'd start the evening at one party, but it was hard to enjoy yourself when you had the sneaking suspicion that the other party was the really cool one. So after a while you'd hop on a bus and head off to the other party.
I celebrated quite a few New Year's Eves sitting on the number 22. And then, when I finally got to the right place, it would be just the same as the party I'd left - except I'd missed all the fun at midnight.
Over time I learned that it's better to commit yourself to one party and stay there, regardless of what you think might be happening elsewhere. For me it's the same with writing projects. It's better to stick with the one you've got, regardless of how enticing another project might seem to be, because it's better to be singing Auld Lang's Syne at a party than stuck on the bus while the rest of the world celebrates.
That first draft you're working on doesn't have to be well written, it doesn't even have to be competently written, it just has to be written, and written until you get to The End. That might mean some bits are pretty sketchy - they might only be in note form - but at least you've got there. And once you've got a first draft, you can always make it better.
There are of course some writers who can keep several projects on the go at the same time. There are also some people who win the Lottery every week. I think most of us know we're not going to win the Lottery, and I think you probably already know if you're the sort of person who can handle multiple projects and see them all through to completion.
I know I can't. I have to accept my limitations, and stick with the party I chose in the first place. I have to commit or I'll end up with lots of projects started and nothing being finished. And the sad truth is, an unfinished piece of writing is no good to anyone.