In trying to make discoveries, we are trying to uncover knowledge of HIDDEN realities. It appears impossible to uncover knowledge of hidden realities. How can we evaluate results? (How can we find out whether they are true or even good approximation when we cannot compare them to the hidden realities?) But we are often able to do things which appear impossible; it depends on whether we have chanced onto, or discovered, or invented, the relevant OPERATING PRINCIPLES. It appeared impossible to fly to the moon in one lifetime. We discovered the principle of the rocket. If we can discover the operating principle for making discoveries, we know how we make discoveries. In this paper, I show step by step how we can discover this operating principle.