Why can't all moths do it!

I've just emerged from my morning ritual of poring over hundreds of illustrations to identify moths from my overnight light trap. I'm getting a bit better at recognising lots as soon as I see them, but certain groups are still a frustrating puzzle. I've even spent time this morning agonising over one which I now think is an Uncertain - yes, that's its name! Then I came to the one in my photograph and my confidence came back - it's a Figure of Eighty...no doubt about that, it's clearly labelled on each wing. Now why can't all moths be labelled like that?!