When you were in school, did you ever forget your lunch at home?
Since you'd planned on eating food from home, you probably didn't bring cash to buy a lunch, so you were stuck without anything to eat. Maybe you watched your classmates dig into their sandwiches, the smell of peanut butter and jelly making your mouth water. When your friends asked where your food was, you shrugged it off and told them you weren't hungry. But by the time you returned from the cafeteria, you were probably shifting in your seat, hoping nobody would hear your belly growling.
Cut to math class where you were likely struggling to pay attention long enough to solve even the simplest equation, too distracted by the emptiness in your stomach to concentrate. Maybe your teacher even caught you daydreaming, and you were too embarrassed to admit that you'd been thinking about what flavor granola bar you'd tear into once you got home.