If you frequently abandon writing projects, we highly recommend Duckworth's Grit, which she defines as:
Duckworth writes that grit is a better indicator of success than "talent" or IQ scores.
We culled from Grit that the success of one book shouldn't be your top-level goal, because you may not be able to sustain grit if that book isn't "successful". Your top-level goal should be to be a New York Times bestselling author or, even better, something altruistic like exposing the injustices of the African's involvement in the transatlantic slave trade or reversing the North American age-of-consent laws, which you may attempt to accomplish through writing books, blog posts or magazine articles. Therefore, writing may serve better as a low-level or mid-level goal.
Here's an animated summary of the book until you can get a copy: