I like to write sad songs. They're much easier to write and you get a lot more emotion into them. But people don't want to hear them as much. And radio definitely doesn't they want that positive uptempo thing.
You want to try and bring a character to life in an honest a way as you possibly can. It doesn't matter whether he's a doctor an actor a car salesman or a captain of a starship. If you can bring truth and honesty to that character then your audience will believe you.