In the end, any story that will showcase your value to admissions will inevitably be able to be backed into one of the Common App essay prompts; because the whole point of these prompts is to help you identify insightful, revealing stories about yourself. In fact, a good personal essay topic often fits within the confines of multiple Common App essay prompt options. You might even identify a new and unexpected spin on your subject while considering it through the lens of a prompt you never expected to use (and may not have even considered in the first place). Over the years, so many surprises have revealed themselves through the Backwards Brainstorm, perhaps most of all that it works every time.
Not just humor, but the overall tone of your application essay is remarkably important. It's also difficult to get right. When you are asked to write about your accomplishments, those 750 words on how great you are can make you sound like a braggart. Be careful to balance your pride in your achievements with humility and generosity towards others. You also want to avoid sounding like a whiner -- use your essay to show off your skills, not to explain the injustices that lead to your low math score or failure to graduate #1 in your class.