This is something that most people don't understand, given that we live in a world where food is cheap and plentiful.
As many people who have gone through fasting-based diets have discovered, there's a difference between "I'm hungry" and "I need calories, I'm getting weak and tired." Learning that difference is how you discover the actual amount of food your body requires, not just checking off three meals per day.
The feeding patterns of our ancestors were very far from "eat as much as you want all the time with no physical effort required," and that was normal for 15,000+ years, so it'll probably take longer than the 100-200 or so since industrial food production began for our brains and bodies to adjust to the new normal. That, or we'll just have to start teaching our kids about cravings vs hunger vs actual food-need.