Thousands and thousands of people write a (short) novel every November for National Novel Writing Month (aka NaNoWriMo). If you haven't heard of it, it's worth googling and joining.

One double-spaced page per day on average (that's ~250 words) is a full-length novel in a year. 250 words is nothing at all.

But thinking about it and hoping for it and wishing for it won't get it done.

First question you have to ask yourself: Do you want to write, or do you want to HAVE WRITTEN?

Those are very different things. A lot of people lust for the finished product, but they aren't actually excited by the idea of doing the work. And it is work. It's a lot of work. Whether you're writing one grand literary novel every three to five years or cranking out a novel every month (or faster...) it is still work.

I and my author friends do the work because to not do the work is death.

So question two is, WHY do you want to write this book?

If it is to prove to someone else you can, or to make a lot of money, or to brag to your friends and enemies...there are other, faster, easier ways to do those things.

If it's because you have a white-hot burning inside you to tell this story, no matter how few or how many may read it...then start writing. You may want to choose an outline plan first, such as Save The Cat Writes A Novel, or Story Engines, or the Hero's Journey, or the Virgin's Promise, or the Snowflake Method...pick one that suits your mindset and start an outline, then get busy writing those 250 words.

To paraphrase Gary Vee: You didn't exist for a very long time. You won't exist for even longer. If not writing a book is something you will regret at the end, then what are you waiting for? If you wouldn't really regret it...then don't worry about it and go do the other things you would regret not doing.

Finally (actually, not finally, there are dozens of other topics related to this question), let's say you do have a story you absolutely must tell. Is a novel the best way to do it? What about a video series, or comic book/web comic, or film, or audio drama, or a zine, or a song or poem, or...or...or...?

You have dozens of ways to tell your story sitting for free on your phone. Try them all, see which one gets you fired up.