Hmmm, you guys are hurting a lot of good fly tyers feelings with this thread.
OK, here's my two cents. (disclaimer: I am an avid fly tyer, so I am not impartial )
Certain factors matter, but not always. So, the GT eating a sandal may happen, but not consistently enough for us to be carefree about what fly we throw.
1)Certain species are more consistently selective than others. Trout can lock in on a fly size, color and type to the exclusion of all else. Permit didn't get caught on flies consistently until great crab patterns were developed. But try using the same crab pattern on a milkfish and see how consistently it works. Other fish are so aggressive, that they often seem to hit anything that moves. But not always. Sometimes even these aggressive species need a certain fly pattern.
2) Presentation may matter as much or more than the fly pattern, but a poor fly pattern often limits the presentation. For example a top water fly that won't float, a sinking fly that is to heavy to throw, the streamer fly that spins or lists to one side, or a fly that needs an effective weed guard.
3) The fly that is closest to the size, color and shape of the most abundant prey, will more often than not produce the most strikes.
4) Angler confidence is a huge factor, and a fly that you think has all the right stuff, is the fastest way to building confidence. A confident angler, seems to make better casts, is more focused, and more persistent than an angler that is unsure whether what they are throwing will work.
So, those one off situations where the fish seem to hit any snot fly that you throw are great. But that means that they will also hit a well tied, well thought out pattern too. Why not just use the best fly that you can, just in case those fish suddenly get finicky?
