Fitzgerald's sharpest advice didn't come in a craft book. It came in letters, often blunt ones, to young writers and to his own daughter. The theme underneath all of them is emotional honesty: you have to spend your real feelings, not the safe ones.

The Direct Answer
Sell your heart, and accept that nothing good comes easy.
His most famous line on writing comes from a 1938 letter to a young writer named Frances Turnbull, telling her she had to sell your heart, your strongest reactions.

Sell Your Heart

In the fall of 1938, a Radcliffe student named Frances Turnbull sent Fitzgerald a short story and asked what he thought. His reply is the best summary of his whole philosophy of writing. He told her the price of professional work was higher than she was prepared to pay, because real writing means trading on your deepest, most uncomfortable feelings rather than the pleasant anecdotes you'd share over a meal. He pointed to Dickens, to Hemingway, and to his own first novel as proof that the good stuff gets torn out of the writer's own life.

You've got to sell your heart, your strongest reactions, not the little minor things that only touch you lightly, the little experiences that you might tell at dinner.

F. Scott Fitzgerald, letter to Frances Turnbull, 1938

The point wasn't cruelty. He was telling a beginner the truth that no technique can substitute for genuine emotion on the page. When you don't yet have the tricks of the trade, he wrote, your feelings are the only thing you have to sell. That idea sits at the center of everything he believed about the craft.

Feel It Desperately, and Expect It to Be Hard

He gave his daughter Frances, known as Scottie, the same hard truth in a 1936 letter. He told her that wanting to be a writer wasn't enough. If she had something to say that nobody had said before, she had to feel it so desperately that she'd find a way to say it that nobody had found before. Style, in other words, comes out of pressure, out of caring intensely about the thing you're trying to express.

And he never sold the work as easy. To Scottie he put it in five plain words: nothing any good isn't hard. He saw talent as a starting qualification, like passing the physical to enter West Point, and the actual writing as the long climb that comes after. Encouragement and a warning, in the same breath.

For how he actually worked, and why his own routine was anything but steady, see the full F. Scott Fitzgerald writing routine.

What You Can Steal