Frequently changing flies is the sign of what? Impatience? A thought out progression of presenting patterns? Giving up on ‘the’ recommended pattern(s) for that stretch of water? You paid $1.75 + for that little gem, why didn’t it work?
On lakes, I change often. That rod is under my left arm/elbow every 10 minutes or so. As I search with trusted searching patterns, if they don’t soon produce, snip, new pattern. I seem to have more faith in searching patterns that fit the standard stillwater food groups. I have an arsenal and I quickly change through it to find the connection. I feel more intuitive on a lake. Some would say it is easier; just find the cruising fish. I think it is presentation, manipulation through the horizontal/vertical pathways.
On rivers, I am more exacting. I study more. I plan upon what insects are in a certain drainage and which stages of the insect’s life are worth tying and presenting. If an insect emerges from the nymphal exo-skeleton well below the surface then in the surface film emerger/stillborn patterns are a waste of tying time. Better to tie wet, soft hackle, flymph patterns that replicate the emerging mayfly well below the surface, but swimming toward the top.
Stream habitat is more complicated than stillwater habitat re trout and their food sources (in my mind). There are often more options on the stream. If the clinger nymph rarely dislodges from the substrate and ‘drifts’, then stocky little nymphs are less useful. I study bottom to top. And, for some fly fishers it is the other way around: Rivers are an open book and lakes are featureless and boring.
Research, then think before just tying on the ubiquitous Hare’s Ear Nymph or Adams Dry Fly and wasting a hundred casts, as the river pulses with life everywhere except on the end of your line. And, again: location, the pattern, then the perfect manipulation/presentation. Random searching patterns are ok, for awhile. But, as you come up empty outing after outing, you will soon decide to learn more (insects, other fish food) about the specific waters you fish. Or, you might develop your own data through in the field observations. Check out a perfect example of this at Winona Fly Factory