Technique is a must, but knowing what is in the water for the fish to feed on is paramount to turning a good day to a great day. Also, you may have the technique down pat and the right type fly on and it will still be hard fishing.
Case in point....
This past spring I was on the Clinch. Sulphers were abundant but no one seemed to be having much luck. I tried nymphs, dries, emergers. Everyone in that part of the river was struggling. Then...on a whim, I tied on one of those flies that I only tied one of...a sulpher nymph with two or three wraps of starling. Wham! I stood in one spot and caught a bunch of fish. The only thing that slowed my day down was when the fly was so tore up that it was unusable. Thinking I had found the key to the kingdom I went home and tied up a bunch...never caught a fish on em since. Go Figger?!