Is Fly Fishing Really All About Imitation By Trout Fly

In any field of endeavour, there are things we don't fully understand. Lack of understanding is often compensated for with assumptions. Such assumptions can sometimes be correct. Other times they are not.
In a number of different activities I have found that by querying anything which doesn't quite make sense, we can locate these assumptions. Once found, analysing them and applying some logic enables us to either come up with a more feasible alternative or, hopefully, the correct answer. Where accurate answers can be found, exceptional results can be the result - and so it has proven in Fly Fishing also.
Our traditional Fly Fishing enthusiast embraces the study of entomology. Flies replicating relevant insects are purchased or tied and our angler is ready to tackle the water.
On arriving at the water our angler might look for a sign of insect life which could lead them to the selection of a seemingly appropriate pattern.
Once a pattern is selected and attached, they start to look for a Trout, or a sign of one feeding.
In position, our angler executes their cast and delivers the fly. The Trout takes the fly and is hooked. The fly selection was obviously correct for a classic deception. With luck, the Trout is landed.
If the fish is to be dispatched, the angler does so quickly. By whatever means, our traditional angler then checks the stomach contents of the Trout to confirm or see on what the Trout was feeding.
So there it is - our angler has done everything right - by the book!
Or have they? They certainly followed the routine depicted in the manuals. But did those events happen for the reasons we thought they happened? If so, why would it not happen that way every time?
Let's just review the process and start by looking for assumptions.
When our angler selected their choice of fly, were they assuming the Trout would be feeding exclusively on the insect imitated by that particular pattern? Possibly, but not necessarily so as Trout rarely feed exclusively on one diet item.
When the Trout took the fly, our angler assumed his fly selection was correct. However, in so doing, they were assuming the Trout would not have taken any other fly at that particular moment. We could never check or confirm that, either way.
Was our angler not also assuming the Trout took the fly to be the insect intended to be imitated? It certainly took it to be food, but we could never confirm it took it to be the insect, or creature, imitated.
I know we see occassional claims that during a particular 'Hatch,' unless you have the matching pattern, you just can't catch the Trout. The reality is that no such claim could be made unless every alternative fly pattern was tried and rejected, and that would be just impossible to do.
When I first started, I also checked the stomach contents of fish but am now at a loss to see what is gained. Possibly it is just part of a progressive learning process but it serves little purpose given that you have already caught the fish. Knowing on what the Trout was feeding can't help you catch it again.
Some would argue that if you know what is being taken it can help you catch other Trout in the vicinity. On the surface of it, that sounds reasonable. However, I recall an occasion way back when I was still checking stomach contents. I caught both of two Trout feeding in quite a small pool. Each fish had a collection of just one food item in it's stomach, but the items in question were different in each fish.
Both food items were available to both Trout so it seems there was some element of personal preference. Traditionalists might argue here for two cases of feeding exclusivity. However, I caught both fish on the one fly which never resembled the items found in either fish.
By checking stomach contents, we are assuming that other Trout will be taking the same food items. That is quite possible, and even likely, but there are no guarantees. Besides, if we could assume that other Trout will feed on what the captured Trout was taking, the logic would then suggest that the other Trout should then take the same fly as taken by the captured fish. So what point in checking stomach contents?
Where does the logic stand when the Trout takes a pattern resembling nothing the Trout is ever likely to encounter in it's natural environment? Has any angler even seen anything resembling a 'Silver Doctor' ( ) in the stomach contents of a Trout? I doubt it. We cover the lack of logic by calling this an 'Exciter' Pattern.
Where then is the logic of a Trout taking a pattern developed around the other side of the globe closely resembling an insect not found in our locality? If that pattern lacks the bright colours of the Silver Doctor, it can hardly be labelled an exciter pattern. Certainly not, so the Trout is merely labelled 'Unpredictable.'
As you can see, even our 'Classic' Scenario incorporates a whole sequence of assumptions, not all of which are necessarily incorrect. I thought there were enough though, to question the validity of the basic imitative approach to Fly Fishing.