Welcome to Writing Biz Reality.
Do you really have to write every day in order to be successful? Aren't there times when it's okay not to write? When the world around you is falling apart? Sure, there are times when you just can't make yourself write, nor should you.
Grief afflicts my creative process. In a short space of time a few years ago, we lost loved ones. Attending one funeral after another isn't conducive to creating fiction that's anything more than an outlet for your personal suffering. I didn't write for a long time.
What I'm saying is don't allow yourself to be easily seduced from your stated goals. Writing a book is like dieting without commitment. If you want to lose 30 pounds but you indulge in dessert every time a delectable sweet crosses your path, will you get to your goal weight?
The same holds true for writing a book. If you know you need to write 4 pages every day to have a completed manuscript in 3 months, how many pages will you write if you get pulled into the living room for TV every night? Not very many.
Most worthwhile goals in life require sacrifice. What will you sacrifice to make time to write every day or every evening? If you can't think of anything to give up in order to have time to write, then the plain truth is that you're not really dedicated to achieving your stated goal.