If we like what we are creating, we don't have to know why. Sometimes the reasons are obvious, sometimes not. And they can change over time. It could be good for any of a thousand different reasons. When we're making things we love, our mission is accomplished. There's nothing at all to figure out.
Our work begins with a seed, which sprouts a trunk of the core idea. As it grows, each decision we make becomes a branch splitting off in a new direction, growing finer and finer in detail as we move further out.