Crush His Head

The Devil has been given power to bruise our heel but we have been given power to crush his head. Yet it seems that this often plays out the other way around. I believe Satan uses every means and resource within his control to bruise our heel, but we do not. Although we have the power to crush his head, at best, we might only be pricking the pads of his feet. If we will hold up the shield of faith and wield the swift sword of the Spirit, we will then crush his head and leave him powerless. So what holds us back from doing so?