Stephen King didn't stop with The Shining, his first hard cover bestseller.
J. K. Rowling didn't stop with the first Harry Potter books.
John Grisham didn't stop with The Firm.
Brandon Sanderson didn't stop with the Mistborn trilogy.
George R. R. Martin didn't stop with Game of Thrones.
All of these bestselling authors (and many more) did one thing in common: they wrote more books.
Of course, there are runaways successes like Harper Lee, William Peter Blatty, and J. D. Salinger who wrote one book (or two in the case of Blatty and four for Salinger) and quit. These are not the norm for most authors who want to have a successful writing career.
Write more books.
Rome wasn't built in a day. I look back at my blog and am astonished at how long I've been doing this. I also look back at when I wrote some of my previous (unpublished) books and wonder what in the world I've been doing.
I am in this for the long haul. I will be writing, and publishing, more books.
Don't treat your writing career anything less than the building of Rome. It may be slow, but keep writing.
The world needs you.