The other popular view on the matter is that they take based upon aggressiveness. When they view a tiny fish in their area they get perturbed and also they go after it. With swing flies the fly will resemble its fleeing the location because of the visibility of a bigger predator and that's when the steelhead strikes. This is the idea behind Spey fishing.
Most of us come from a trout fishing background as well as are relied on to fish acting in an instead predictable way. If there is a caddis hatch taking place and also you can literally see trout proactively feeding for caddis there is a great chance that if you make use of a pattern mimicing a caddis you're going to capture a trout. There is a direct as well as apparent correlation between just what fish are living on as well as just what will provide you the most effective chance for success.