How can I add insight/a so what to my common app essay?

This question is difficult to answer because it goes on a case by case basis, and each person will do this differently depending on the story they're telling. If you're doing Prompt 5 which is specific to an experience sparking personal growth, you'll want to choose an experience where you have a lesson that you learned, and throughout the essay hint at/explain the lesson indirectly with some conclusion and connection to the future at the end. One example from a YouTuber who got into Brown was that they had stage fright in debate and took off their glasses to solve it (they couldn't see the faces in the audience), but ended up debating better with their glasses on because when they looked into people's eyes, they were able to connect with them more and that made them a better debater. Throughout their story, they were able to allude to the ending lesson with that realization at the end.