Then the question once again applies; what is actually moving? The string isn't moving, it is still but forces make this still string move, and those forces too are caused by forces. It's as if nothing moves except for pure potential energy.
I kinda get the same idea. I start to think instead of asking why something rather than nothing I would ask, why on is default instead of off. Then we ask what is on? Is there a positive balance of energy or action in the universe?