CONVENTIONAL WISDOM SAYS that, if you want to reach a goal, you should share it with people, so they can help hold you accountable.
I'm not sure that's the best idea with a novel.
For one thing, some psychologists say that the whole idea of sharing-to-motivate can backfire. If you say you're becoming a novelist, people who love you may praise you for doing that, and the gratification that results can play a trick on your psyche: in your mind, you have already accomplished what you are being praised for, and so become less inclined to actually write the book.
At the other extreme, people in general have no idea how long it takes to write a novel. So if you share your goal and, four months later, people ask how you are doing and you say you only have three chapters written ... the look they give you may so discourage you that you give up the entire idea.
And finally, writing a novel is an intensely private act that results in a very public outcome. Oftentimes, inviting others into that extremely private space just somehow seems wrong. I know that, on those rare occasions when I've been able to keep the news of a novel-in-progress to myself, I've been happier in my work.
So ... are you writing a book? That's great.
But you just might want to think before you go sharing that news with all and sundry.