Think of your body as a 3-stage rocket and your cue as the payload.

The first stage engine is your lower body – legs, hips, back. They accelerate your entire body forward to a certain speed. The second engine then fires – your shoulder, upper arm and forearm begin accelerating forward. At the last split second before impact, the third stage fires. Your wrist comes forward and your fingers tighten their grip on the cue, snapping it forward at maximum speed.