When did THIS happen?

When you’re a kid you must eat all of your dinner if you want any dessert.

When you’re an adult it’s required that you NOT eat your entire dinner so you can save room for dessert.

Did this come with turning 21 and the ability to drink legally and I missed it?  Or did it come with a specific life event – say putting on extra pounds while eating and exercising the same amount as before when it didn’t cause you to get wider?

Interesting.