Although dry fly fishing for me is what I consider to be the ultimate for the sport, must confess that I've caught more trout under the surface with nymphs, streamers & scudds ~ maybe a ratio of 3 to 1.
There is a phenomenon about going underwater, especially (but not limited to) streamers. Everyone knows when a good sized trout takes a streamer hard ... there's just no doubt about it. However, sometimes (and I don't know if this is when Mars lines up with Jupiter, or the moon gets full or what), especially with browns, they will just bump the streamer, giving the impression that it's a small fish doing the bumping. But sometimes a few determined casts and presentations will reap a good sized trout that's been doing the bumping!
Dale