Getting the printer to pick up a single sheet off a stack of .003” thick sheets at a variable depth, and then dealing with variable sized-sheets, rotation, paper jam detection to avoid burning out motors, just to name a few. Things get even more complicated with things like 2-sided printing.

If it was just one of these at once, it might be pretty approachable, but the classic and convenient 8 1/2 X 11” paper tray that modern printers have is a genuine challenge to manage without lots of careful communication with all the different parts.