A lot of that stuff is internal industry knowledge that people learn by working for a company that already does it. It probably started out with people experimenting. You don't learn that in a mechanical engineering degree.
Though printers use rubber rollers on the top sheet in the pile so the friction between the rollers and sheet is greater than the friction between sheets and therefore only the top sheet is fed by the rollers.
...and often a second roller on the underside, slightly forward and running in the opposite direction to strip off any sheets that adhere to the top one.
Though printers use rubber rollers on the top sheet in the pile so the friction between the rollers and sheet is greater than the friction between sheets and therefore only the top sheet is fed by the rollers.