Many people produce things with their hands, or rather, parts of things. An assembly line worker helps to physically build part of a car or whatever it is that his factory produces. There is nothing wrong with this, many things would be hard if not impossible to mechanize, and some actually enjoy this work.
Now for the part that no one here likes to talk about: Intelectual production. If the same factory worker that we just talked about had not been supplied tools and instructions, he would not have been able to do his job. Even if he had been given these things but they were not correct, he wouldn't have been able to do his job. Guess who supplies him with those things. Did you guess that it was those evil people from up the ladder? Maybe even the President or CEO of the company? You were correct. WIthout having the line thoiught up, without having the people hired, without having the correct tools and instructions, among other things, many factory workers wouldn't be able to perform their job.
Perhaps this explains why it is fair for people up the ladder to make more money, even though they aren't physically making the product.