Allusions:
Because in the Spring and Autumn Period, monarchs of all countries were vying for hegemony. They often struggle for many years but get nothing, as if they had a long dream, so they had a big dream in the Spring and Autumn Period.
There is also a saying that during the Warring States period, the goal of Qin was very clear, that is, to destroy the six countries and unify the world, while the goal of the other six countries was still to unify the world. They were still dreaming about the Spring and Autumn Dream, so they had the Spring and Autumn Dream.
Now some people say unrealistic ideas, and people often say "fuck your spring and autumn dreams" to satirize him.
Extended data
The Spring and Autumn Period is the first half of the Eastern Zhou Dynasty in China's history. The historical period from 770 BC to 476 BC is called "Spring and Autumn Period". The hegemony war in the Spring and Autumn Period brought all kinds of disasters to the society. However, in the process of hegemony, some countries were eliminated and some bigger countries appeared. It laid the foundation for Qin Shihuang to unify the whole country later.
References:
Baidu encyclopedia-Spring and Autumn Dream