My filing cabinet has a moveable thingy which is like a very thick wire in a kindof sortof V-shape. It fits into slots on the edges of the drawer, which are spaced about every 2 inches along, and is also held in place by ridges along the bottom of the drawer. I put it (ideally) a few inches behind the last folder so there's a bit of looseness allowing folders to be slid in and out easily. You could just take some cardboard or string or strips of wood and attach them to the drawer with sticky tape. Or maybe a cardboard box as suggested by GMX, although you have to be ready to switch in a differently-sized box as your amount of folders changes by more than a few inches, or cut pieces off the box.
Inability is an abstract thing involving comparison with alternate universes; it cannot be experienced.