Excuses, Excuses
It's tempting to focus on the product launch, on the interview, on the next thing. Tempting, but ultimately a waste.
Finishing a book is a lot more important than starting one. Why? Because lots of people start books but never see them through to completion. There are lots of reasons why, but here are the most common.
The Big Stall Out
You rewrite and you edit and you tweak and tweak and tweak the first few chapters, aiming for perfection. Not that perfection is wrong, mind you, but when it causes you to not make any forward progress, then it is wrong. Stab the inner editor in the heart and finish the dang thing.
It's Too Hard
Writing is work. Hard work. It's easier to say you're a writer, to dabble in a paragraph here and there, than to sit your butt in a chair and complete a manuscript.
Too Focused on the End Result
Dreaming of publication, hanging out with authors, scheming out your launch party, these are all fun to think about but if you don't actually write the book you won't attain them.
Fear
If you never finish your story then you won't have to show it to anyone. It's frightening to think about exposing your words to the world because the world is a scary place. Now's the time to buy a pair of big girl/boy pants and suck it up.
"No" Isn't Part of Your Vocabulary
In order to say yes to writing a book, you have to say no to a host of other "fun" activities. Writing takes time -- time away from other things you might want to do. Ultimately it's up to you to schedule your writing time and guard that time like a beast.
Do yourself a favor and finish your book. You'll feel like a champion even if it never makes it to publication.