Why can I have two loaves of bread for breakfast but not a full meal for lunch?

This is actually related to the lifestyle and eating habits that everyone has developed for a long time. Like most people in China, they usually have a small breakfast, a full lunch and a good dinner. Because most people have to get up early for work and school in the morning, they don't have much spare time to cook a big breakfast. So I am used to dealing with it in the morning. At noon, because I have some spare time, I eat less breakfast, so I eat more in revenge. So you will feel full if you eat casually in the morning, but you will eat a lot at noon.