You can get your fly to the fish in the stream or river but the fish just won't take it. Why not? Your dry fly or nymph is not moving down the stream at the same speed as the current. The dry fly is creating a wake on the surface or the nymph is speeding past natural food bumping across the bottom of the stream. Both look un-natural to the fish and will not be eaten. Intermediate casters can learn presentation casts to give your fly drag-free drift which makes your fly or nymph drift naturally. Whereas before you achieved one metre of drag-free drift, now you can drift your fly for five or six metres. Which cast will catch more fish?