Hatchery trout aren't so much dumb as they are ignorant. That's important because for many people the opening of trout season means trying to catch newly stocked trout. These are fish that might not eat the most artfully presented artificial nymph simply because they have no experience with the natural food it represents.
That's why you'll often have better opening-day luck with a flashy streamer pattern or a Mepps spinner or even a worm. Recently stocked trout often respond very aggressively to something that moves and flashes through the water. And the scent of a worm can bring an immediate bite. But not a Light Cahill dry fly. Huh? What's that?
I'm not knocking trout hatcheries here. I'm lucky in having wild-trout streams nearby where no stocking is done. And there are others also nearby that are stocked generously every spring. When I'm really desperate for a yank on my line, I go fish for stockies. When I'm looking for more of a challenge, I fish for wild trout. Not everyone has that choice, however, and if stocked trout are what's available in your neighborhood, I hope you're fishing for them instead of turning up your nose at the idea.
Hatchery fish do learn after a while, of course, and can become increasingly difficult to catch. As they become acclimated to a river or lake, they learn to focus on natural foods. Fishing pressure counts, too, and trout that have been caught and released a time or two become doubly wary.
A brown trout that spent its first two years in a hatchery trough followed by a year in your local river has become a most worthy opponent--probably as much so as the most wily stream-bred fish.
There are other issues pertaining to trout stocking, which can adversely affect wild populations if introductions are made on top of stream-bred fish. But in those many rivers of marginal water quality or those that become too warm for trout later in the summer, stocking can mean the difference between fishing and no fishing.
Meanwhile, take pity on those poor, ignorant hatchery fish. Give them what they already know and love--a PowerBait hatchery-pellet imitation, perhaps, or the bright flash of a Phoebe spoon. And save all those fancy trout flies for later in the season when you'll really need them.