The essence of fly fishing is to out-trout the trout. It isn't deceptiveness that is needed, nor a mastery of some formulaic set of rules.
Trout face upstream.
For example, an underwater ravine will narrow the water channel and concentrate the surface pattern into a rapid, steady conveyor belt of tasty insects. But to counteract the current and maintain one's position in such a location would require vast amounts of energy, and to do so mid-river would render one vulnerable to hawks.