system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: How did we come up with the idea of three meals a day for a normal family?
gpt
Breakfast was a recent invention. During and before the middle ages, nothing could be eaten before morning mass. The meal was essentially invented during the industrial revolution for labourers.

Lunch pretty much existed forever, and was the main meal of the day - big hearty lunches. It was only until the industrial revolution when lunches started to become lighter, due to labour.

Dinner was originally a lighter meal, but again, because of the industrial revolution, the big hearty meal of lunch had to be pushed later into evenings as dinner.

This is all European history though; if you are Chinese, you might have a breakfast, a 4 o' clock meal and a very, very late supper.

EDIT: China is a very large place, you'll probably see different traditions on when people eat within different parts of China.