Does the essay have to be about a specific incident or event?

All the Common App essays I see seem to be about a specific life event or experience. My essay, on the other hand, pretty much summarizes the past four years of my life–it doesn’t focus on a particular incident, is that okay? I’m using the first prompt: "Some students have a background integral to their identity…

That’s fine, as long as the essay has some sort of clear, unifying theme, that X,Y, and Z all contributed to _______ which is important to you because _______. I can be hard to condense and integrate so much information, but it can be done, I’m sure.