Suppose you know with 100% certainty that fish are located in a certain area. With the perfect presentation, let's say on a particular cast you have a 40% chance of inducing a strike. With a suboptimal presentation you may have a 20% chance of inducing a strike. With a poor presentation, you may only have a 5% chance of inducing a strike. The numbers are obviously made up, but you can see that a better presentation will improve your "luck."