From “Just. Keep. Writing.” by Victoria (V.E.) Schwab (with bold emphasis added by me):
The fact of the matter is, if you’ve written a book, and it doesn’t sell, and you want to keep going, you need to write another. If you’ve written a book, and it does sell, but doesn’t do well, you need to write another. If you’ve written a book, and it does well, you need to write another. All roads lead to writing.
And this is good, because when it comes to publishing, very little is in your control. But the one thing you CAN control is the book. The words you put on the page.
So when everything is going well, and when everything is falling apart, you have to keep writing. It is your tether in the storm, and your grounding when you might otherwise float away. It’s easy to lose focus, to get caught up in the successes and failures, but you must. keep. writing.
Your greatest asset is your writing. But almost equal to that? Your endurance, your fortitude, your belief in yourself.
Both links are very much worth reading in full.