One of the rare highpoints in Hemingway's published correspondence is his 28 May 1934 letter to F. Scott Fitzgerald:
"Forget your personal tragedy. We are all bitched from the start and you especially have to hurt like hell before you can write seriously, But when you get the damned hurt use it--don't cheat with it. Be as faithful to it as a scientist--but don't think anything is of any importance because it happens to you or anyone belonging to you."
That's the most often quoted passage, but there's equally good stuff in the rest of the letter (written on the occasion of Hemingway's reading of Tender is the Night, about which he says, with typical helpfulness, "I liked it and I didn't like it").
"...good writers always come back. Always." Thus spake Hemingthustra. This is demonstrably untrue, but it's interesting that Hemingway needs to believe this. It tells us more about Hem than Scott.
"You see, Bo [Hem's nickname for Scott], you're not a tragic character. Neither am I. All we are is writers and what we should do is write." The good common sense of that last sentence is cruelly negated by the abysmal character judgments in the other two. Within ten years of the letter, Fitzgerald would drink himself to death; Hemingway, on the other hand, would commit suicide the way a character in The Sun Also Rises went bankrupt: gradually at first, and then suddenly. But again, it's telling that Hemingway needs to believe this about himself.
"Invention is the finest thing but you cannot invent anything that would not actually happen. That is what we are supposed to do when we are at our best--make it all up--but make it up so truly that later it will happen that way." I especially like this one. It reminds me of a story Hemingway surely knew: when someone remarked to Picasso that Gertrude Stein looked nothing like his portrait of her, Picasso replied, "She will."
"Scott for gods sake write and write truly no matter who or what it hurts but do not make these silly compromises."
"You can study Clausewitz in the field and economics and psychology and nothing else will do you any bloody good once you are writing. We are like lousy damned acrobats but we make some mighty fine jumps, Bo, and they have all these other acrobats who won't jump."
And then Hem's attempt at friendship-saving irony: "Jesus its marvelous to tell other people how to write, live, die etc."
I also like the way Hemingway's pen/mind slips twice and he writes 'right' for 'write.' The same thing happens to me whenever I right about righting.