How Does A Electric Shock Start?

Electricity has a natural attraction to the ground. This is the means by which we control it. In a lighting circuit the power comes into the fixture on the black wire and the resistance of the filament in the bulb causes intense heat, which in turn makes light. The power that is not used in this process then travels back out on the white wire and back to the power companies ground. Now, when a person takes the place of the light bulb he becomes the point of resistance for the power and since we have many different kinds of metal in our bodies we conduct electricity, but we are not very efficient at it, and the result is that we are the electricities path to ground. Depending on where we are touching the hot wire and the neutral or ground wire dictates it's path through our bodies, and ultimately the  force of the shock we feel.