You don't want to write a big comment that tells others how to make a change they might want to make, because you don't know what change they're going to want to make. Better to have the attitude that you can't help future programmers make their changes. All you can do is make it easy for them to understand what you were trying to do. And it will be easiest for them to understand what you were trying to do if you were very careful to not try to do too much.