The point is you don't have to. You instead just look at the boxes a few years latter and if at a glance you see one box with few/no dots you know it is safe so you spend just a few seconds thinking about only that box - then you move on to something else. Sure there might be more boxes you can get rid of, but you only need to do one box at a time when you have a few seconds. (or you look at the box and decide you are not ready to get rid of that so you put a dot on it making it less likely this one will come up next time you have a few seconds)