Suppose there is a factory, or maybe a bottling plant, that is fully automated. Everything, from the input and mixing of raw materials, to the manufacturing of containers, and filling, sealing, labeling, and packaging are all done entirely by automation—there is no human involvement from the time the process begins until the finished product rolls out of the plant on a conveyer belt where it is loaded for shipment outside the plant, at which point, the product is finally handled. The production equipment and process is monitored and programmed by someone in a separate part of the facility who checks the process through video displays and instrument readings receiving transmissions via wireless feed to the room. The operator makes adjustments to the production to meet customer orders by wireless remote controls.
Let's say you bring in a visitor who knows nothing about electricity or modern manufacturing equipment or automation—perhaps someone from an isolated, primitive culture where everything is still made by hand. You give this visitor a tour of the manufacturing plant. He gets to see the entire automated process, but he doesn't get to see the operator in the control room and he doesn't get to see the loading of the finished product outside the building. You tell him, "Look at this wonderful process and product man has created." The visitor, who has not seen anyone having anything to do with the production, but rather has seen only mechanical equipment creating the product declares, "There is no person involved in this process. There is no need of any person in this process. Man has nothing to do with this production!" Your statement doesn't fit the visitor's idea of how things are made by people. From what he can see, the visitor is correct—the product is made by machines, not people. Yet, you would also be correct in your statement. Now the visitor notices the changes in the process, for instance, the changing of beverage from cherry to lemon-lime, or the change in container size, but now being convinced there is no human involvement, the visitor just assumes that changes are somehow also controlled by the equipment itself, or control-adjustment is somehow built in to the equipment (which, he might assume, has also been fabricated and assembled soley by machines). Perhaps, after a certain number of units of one type are produced, he assumes the production automatically switches over to a different type—or perhaps it's some kind of accident (he doesn't know of any purpose behind the changes because he doesn't know about the customer orders). The visitor can come to understand the principles of mechanics, and be able to calculate production rates, and can eventually understand the entire production process, but never having seen the operator or control room, has no reason to believe there is human involvement.
To the visitor, the simplest explanation of this process doesn't involve any person because there is no evidence of it or any apparent need for it. All he has to work with is what he can see, and he sees a wonderful manufacturing process performed only by mechanical equipment. He has only your word that there is human involvement in this process, and it runs counter to what he observes and to his experiences.