Give an example of a time when you did something you thought was really good only to find out it was not what your teacher wanted? How could this have been avoided?

Last week I had a college essay to write for my English class. The essay wasn't bad. Of course I put a lot of thought into it but, I strayed off topic unfortunately. I spent a couple of hours writing that essay and making it as detailed as I could. It could've been avoided if I didn't over-think it because that's one of my weaknesses and is really a problem.