Analysis: What's Up With the Title?
Unfortunately, the title makes absolutely no sense. That is, until you've read the story – and even then it's a little complicated.
First of all, it's the "short happy life" and not the "short, happy life." The difference is the glorious comma, and this is not just some error caused by a lazy editor. Not having the comma just means that his happy life is a short one. Having a comma would mean that his life was short and happy, which isn't true: he is only happy at the very end; therefore the part of his life that was happy was, alas, all too brief.
Wait. There's more. The title also has a tinge of irony, because it gives us some expectations that are quickly dashed the moment we settle in to read the story. When the story opens, things are more than a little gloomy. We think, "Hey, where's the 'happy' we were promised? We want our money back!" But as long as we're patient, we'll realize that the "happy" comes later, at the very end, and that it does not last long before poor Macomber gets shot.
One final interesting tidbit about the title: for the movie version of the story, the title became "The Macomber Affair" because film executives thought the movie would sound like a comedy, rather than a drama. Plus, though this might not have occurred to you either, the execs were afraid that a male audience wouldn't like the name Francis. Too girly, perhaps? In any case, at least his name gets a starring role in the original title, thanks to Mr. Hemingway.