After reading “Reading the Water” by Dave Hughes, I believe (at least some) large trout are large trout because they were aggressive feeders when smaller and somehow avoided predation. During that time, they probably repeatedly got pushed out of the prime lies that provide everything a trout needs; comfortable temperature and oxygen levels, shelter from strong currents, protection from predators, and an abundant food source, by bigger fish. But at some point, for whatever reason, they became the big fish that can push out the wanabees. So yes they may have then become more cautious, but they’ve also got protected front row seats at the trough so they don’t have to be so aggressive. We can catch those fish when we can recognize prime lies, and can make good presentations to the fish that will be in them.
Trout are vicious predators. They will eat (or try to eat) any little buglike thing that comes along. (Design of my Tenkara flies proves that) In my favorite stream, using 5x tippet, I catch 7 to 10 trout per hour on a regular basis. This is regardless of which fly I choose. I use tippet purchased from Tenkara companies just because I like the small spools and the artwork and supporting Tenkara companies. COULD I catch more with flouro tippet? Maybe. Do I care? No. I’m delighted with my usual success, casting upstream and getting the best possible drift - varying the depth when I think it’ll matter and picking apart the pocket water of the Western Sierras. Of course I collect and dispose of any fly line that I find in my streams…
I have a friend that calls the native Coastal Cutthroat Trout (CCT) we have here in the PNW on the west side of the Cascade Mountains “an honest fish” meaning easy to tempt with dry and wet flies. I generally agree with his and your assessment. It’s unknown why some of the fish hatching from the same redds and parentage as permanent freshwater resident fish, may migrate into saltwater estuaries and back throughout their lives as “Sea Run” Cutthroat (SRC) and grow quite large from feeding in the abundance that the salt provides.
I have spooked CCT in a small coastal creek near home. On one occasion I turned a corner in the creek and watched two fish just 10 ft away in 12"-14" deep water streak for the cover of the undercut banks.
I was curious and glanced at my watch and froze. Some time passed and first one fish emerged from the bank, and then the other, both taking up stations nearly beside each other on river right over a walnut-sized substrate. Another quick glance at the watch showed about 5 minutes had elapsed. I had kept my Foxfire rod in my casting hand ready, and with minimal motion flipped out a not so elegant cast upstream. The fly according to my log was Red Head-Red Butt Futsu Pheasant Tail Kebari that was a holdover on the line from my previous trip landed a few feet upstream of the fish and did not spook them. As the fly got close one of the fish darted up for it. A quick hookset to stick it followed up by a 2nd deliberate but controlled set and the fish was securely hooked. I brought it quickly to the net.
On another occasion at a small coastal river, I was fishing a Takayama Pheasant Tail Kebari that just seems to work everywhere with a Tungsten Olive Ice & Partridge Spider dropper that has never failed to fool at least one fish per trip on what is normally a slow run that in low CFS conditions had slowed to almost a pool about 3 ft deep. I saw a rise near a submerged log and cast upstream of the log and let it dead drift down beside the log. In the very clear water, a rather large fish (SRC?) swam lazily up from a lie under the log, closely examined the flies, then turned and slowly swam back to its lie 
. That to me is the fish equivalent of an obscene hand gesture. Follow-up casts using sasoi would not move it from its lie 
.
As I mentioned above these larger fish occupy the prime lies where they have the current continually bringing food up close to them, along with protection from the current, and obscures them from predators above. The slow current not only allowed me to get a good look at the fish but probably also allowed the fish a good look at me even though I was in camo from head to toe. The larger fish at the front of the food trough seem to be less inclined to expose themselves and strike at just “anything”.
Nice story… I think that a Trout usually doesn’t have time to inspect what we offer before it sucks it into it’s mouth. I was impressed by a video I saw of a trout, sitting in slower water and having faster water bring it food and non-food particles. Time after time a black speck would come towards it and it would leave station, suck it into it’s mouth and instantly either spit it out or swallow, depending on whether it’s tongue told it that bit was “food” or “not food”. Shows how important it is to set the hook at any little bump. There is very little time before the trout, tasting “not food” spits out your Kebari. I do think that, in slow water, a trout will spend a bit of time looking at your offering - only in that circumstance does it matter how much the fly LOOKS like the “correct” bug.
Comparison of lines ygk pink 3.5, shimotsuke green 3.5, 13 pound 100% japan fluoro and dragontail orange 3.5
Definitely can tell why I like the ygk pink for the ability to see it. Least translucent but i dont lay my line in the water very often.
That pink really pops, and can see it when it’s used on some videos. I tried DT orange and despite the amount and depth of contrasting greens here in the coastal PNW, it was disappearing when I and the line were both in a shadow, but the line was backlit with sunlight; happens a lot in the heavily forested areas I fish. Long ago I read that the color red (pink, orange variants) is the least visible in dim light. So I tried the Yamatoyo yellow that has a slight greenish tint. It is almost the same color as used on fire trucks in some locales. I found it remains visible in most lighting conditions. I tie a section of 0X Orvis chartreuse-orange-white sighter on that I can almost always see when the yellow washes out. @Lkn4trout mentioned
And while that SRC I mentioned above took a leisurely look at my flies in low, slow, and clear water then slowly swam away, it wasn’t spooked. Rather it was smart.
I can’t say that my highly visible lines kept off the water haven’t spooked fish, just not enough to use less visible lines.
I think I have some of that pink and may try replacing one of my remaining DT orange lines I still use to see how it works.
There are some situations where line color matters very much. Heavily pressured places like my South Platte, with low and clear water and you are actively working the fly. Having line jump around will not only put down fish during sunny times, but the catch rate is pronounced between anglers using other color lines.
Hi Matt, I have some of that Stealth line and still use it in making up tapered leaders. It’s color is a sort of opaque, pale milky green that is surprisingly pretty visible to an angler but does not spook fish that I have been able to tell. Put a black light on it and it lights up like a lantern as a very bright Sky Blue. The line was made and developed in Japan. I believe the reason it was discontinued was because it did not sell well enough to continue making and selling it…Karl.
A fairly new development in competitive Euro Nymphing Sighter Leaders has bin the use of the previous segment’s tag end to be a Dropper that the desired fly pattern is tied directly to. The sweet spot is in the 3 to 4” long range to prevent the flys from wrapping around the main line in casting and fishing. If World Class Competitive Anglers are tying their flies directly to the brightly colored Indicator Line sections and successfully catching as many fish as they can with them, I do not believe we Tenkara anglers need to be overly concerned about our highly visible level Tenkara lines spooking fish…Karl.