You would no the watch has a manufacturer because YOU as a human being are the manufacturer and you know there are many other human beings out there as you see them, speak to them and hear them all the time. However if you were the only human on Earth and had never ever seen anything mechanical before and knew of no other humans then you would think that it was something natural.

"We submit to the majority because we have to. But we are not compelled to call our attitude of subjection a posture of respect." Ambrose Bierce