David M recently mentioned ambition and genius, among other things. I've recently finally gotten back to reading Julie P's Tiptree bio, and just came across this quote, from a letter from Tiptree to a young Craig Strete:
[The "genius horse"] knows it is his destiny to make one great burning leap and carry you to shine forever among the stars. To your rightful place. He will chafe all his life at his inability to do this, at the idiotic small steps necessary even to shoulder among the earthly throng, [...] the endless miserable mechanics of attaining even a modest writer's career. Between that and the one great soaring leap he needs the difference is always almost too much.
Phillips adds a comment (talking about Alice Sheldon years before writing the abovequoted letter):
Between Alice and that "great soaring leap" also came a sense that she wasn't ready, that she was still learning and preparing for the great work yet to come. All her life Alice would love new beginnings. She threw herself with enthusiasm into each new job, study, marriage. But when the future arrived with its limited potential, she tended to get restless and move on.
--James Tiptree, Jr.: The Double Life of Alice B. Sheldon, by Julie Phillips, pp. 64-65.
Then again, on the other side of the ambition question, there's what Swanwick said about Gibson and realistic ambitions.