Otherwise it would be like a piece of floppy plastic. If you want to really give yourself a headache, cut a wing in half lengthwise and tell me what you see. It compounds the problem still further. At long last, I'm close to having it licked, but not by thinking like a fly tier. I know that sounds cryptic.
Inspiration can come in the most unexpected of ways, at any time.
You've got to keep alert. Ingenuity, great daring, and imagination are needed when you start tying realistically. Almost certainly, you will become confused by what is or is not fly tying. All I can tell you is to form your own conclusions, then take a stand. Don't let others decide for you.