Where Does the Mechanical Lifting Force of a Lever Come From?

The principle of the lever is one of the oldest in human history. The force applied at one end of a lever (called the effort) results in a force at the other end of the lever in order to lift a load situated there, the weight of which exceeds the size of the effort. Where does the mechanical force which lifts (or otherwise moves) the load come from? An answer to this question is presented.