That U-shaped loop of fly line will continue to unroll in the air only if one end is anchored. At the completion of the forward casting stroke, the rod hand is stopped in an instant. The rod unbends, propelling the line forward, and the tip then also stops abruptly. At this moment, the loop is formed in the air, and the rod becomes the anchor. The sharper the stop, the better the energy is transferred to the unrolling line. Conversely, whipping the rod forward with no stop robs the cast of its power, no real loop is formed, and the line will most often collapse in a pile.