A great book may be an accident, but a good one is a possibility, and it is thinking of that that one writes. In short, to achieve. The rest takes care of itself, and so much praise is given to insignificant things that there is hardly any sense in striving for it.
In the end, writing is like a prison, an island from which you will never be released but which is a kind of paradise: the solitude, the thoughts, the incredible joy of putting into words the essence of what you for the moment understand and with your whole heart want to believe.
James Salter, "Some for Glory, Some for Praise" in Will Blythe, ed., Why I Write: Thoughts on the Craft of Fiction (1998).