Persistence is a necessary quality when writing a novel. Not to mention when I want to write a series of novels. But something else helps me as well.
I've read in several places now that it's a bad idea for writers to discuss their work in progress with others. I understand the concept that in speaking about your plot or characters you may dispel all your writing energy. In verbally telling the story you may lose the impetus to write it. I disagree, for me anyway.
I find that when I am writing a novel having a brainstorming session with my critique group is immensely helpful. Different viewpoints help the process. If I am stuck the other writers can offer ideas about how to smooth out plot points. If I share a few pages they may note where something isn't working and offer ideas for fixing the problem. Just discussing the general story with two other writers who know my book and know my writing style can unearth a whole array of new scenes that will create a more engaging story.
All of this, rather than depleting my writing energy, expands it in all directions. The new ideas spur even more ideas and jettison me to my notebook. The suggestions often save pages and pages of prose that would end up getting me trapped in a corner that would require chapter after chapter to extricate myself from.
Of course you need to do what works for you. If you think you will lose the motivation to write your story by sharing it too soon, then I suggest keeping it to yourself. For me it acts as kindling to get the writing fires glowing.
I happen to love my monthly critique group meetings and our twice yearly retreats. The collective group energy is fantastic!