It's earned the reputation as a junk fly but I dont think that is the best label for this pattern. Admittedly it is not the prettiest looking fly but they catch a ton of fish. I cannot tell you exactly why they work...but they sure do work well. Every angler has their preferred junk fly and mine is the Mop. I caught my personal best Farmington River brown trout with a Mop fly in the Greenwoods Pool.  I had it paired with a very realistic Pheasant Tail pattern, but the fish decided it would rather eat my favorite junk fly, the Mop.