I suspect some of the success of a particular pattern, or lack thereof, has to do with how an angler uses/works/presents it.
I have a buddy who I've fished with for over 20 years. We've learned from each other, and have very similar fishing styles. Yet, there are some lures (in this example, since we started out with spinning gear) that I catch a LOT of fish with, and some that he catches a lot of fish with...but when we each try the other guy's great lure, we catch very few or none. And that is standing next to each other, casting into the same areas. Its a weird phenomenon, and I'm sure the same thing occurs with fly patterns.

This is a good thing, IMO...that means not every angler will be showing the same flies to the fish all the time.