This is a quote I remind myself of a lot, because it's important, but for the life of me I can't find a source for Hemingway ever saying this. I think it was at

This is a quote I remind myself of a lot, because it's important, but for the life of me I can't find a source for Hemingway ever saying this. I think it was attributed to him before even before Kingsmen: The Secret Service but I'm not sure?