The sense of betrayal we feel when staring into a suddenly empty Pringles tube is almost as palpable as the inevitable stomachache. So why do we feel the impulse to eat, even when we’re not hungry? from SciShow explains there's a difference between hunger and cravings.
Hunger sets in when your stomach is empty (you knew that!). Your blood sugar drops, and your body pumps out the hunger hormone, ghrelin, telling you it's time to eat.
Cravings, on the other hand, are almost entirely psychological. So next time you find yourself staring longingly at the newest ice cream shop in town, realize that even though you want three scoops, one will probably satisfy your mental itch.