Another no luck good luck story.
Oh yah, can certainly recall times like that, an exercise in frustration to be sure, especially when trying a new lake.
What to use. Damn......okay, time to start thinking like a trout.
Went to Johnson lake, first time there and the fishing was slow, early in the spring, cool weather, not much of any hatch to speak of, so tried trolling around using a leech pattern for a couple of hours no action at all.
Thought I'd go to one of the shoals and see what was happening there. Saw a few cruising around the bottom so what the hell at least there's a couple fish swimming through, maybe I can entice one to take something.
Tried like you said maybe fifty different flies from Pheasant tails to damsels. Not a bleedin' sniff. Okay time to have lunch............where's the cooler?
Crack open a beer and watch what's going on. (no solid lunch at that point, liquid lunch !)

While sitting there, watching a couple of trout cruising the bottom I saw one tip on it's side open it's mouth and chow down on somethin', at the same time I saw a chironamid come off the water.
The light bulb went on,
I can't beleive what I did next, actually put down the beer

tied on what I thought was a close size and laid that out over the water. Doing half inch stripping , got a couple of taps but nothing serious. So continued the patience and finally hooked a trout, after my frustration of a couple of days of no trout had to see what was inside, sure enough it was stuffed full of chironamid but not like the black one I was using these ones
were a very pale green. Searched through the flybox and tied one on and Holy Crap did that make all the difference, it was chronny heaven !!
Patience can be a virtue although its a pain in the ass !!
............QM'r