the metal you interface with must be connected to earth ground, otherwise it is not providing a path of lesser resistance than the component you are carrying, thus causing a static discharge into your precious hardware. it is possible to have a current in the situation you described (what most people will say is "not completing the circuit") but not at any normal or usable range, which is why the conductor you are touching must be connected to earth ground to start the flow of electrons instead of continuing to build a static charge. think of the earth as a giant bucket and the electrons as water...you have to have a way to pour the water in the bucket, but the only way the water will go into the bucket is through a conductor, and if the conductor is not somehow connected to the bucket, then you will continue to hold the water until it spills over and breaks your ram or video card (assuming you are touching one of those when you literally discharge your static build-up, but you get the point i assume).