During the printing process, the continuous rotation of the extrusion motor will attempt to push the consumable into the nozzle so your printer can continue to extrude the plastic. But when you try too fast printing speed or squeeze too much plastic, the extrusion motor will eventually slip because the Drive Gear can't catch the consumables because of too much wear and tear on the consumables. If your extrusion motor is spinning, but the consumables are not moving, it may be the reason.