What does it mean to be cool under a big tree?

This sentence means that with reliance, things will be easy.

This sentence comes from the first fold of Yuan Anonymous's "Licas Marry Maids": "I eat his food every day, so I can enjoy the cool under this big tree." This idiom is often used to describe that a person or a group has strong backing or related help in daily life. "Big trees" are often compared to powerful people or groups, while "enjoying the cool" means gaining benefits or being protected.

In real life, we will find that many successful people and groups have strong backing or relationship help. For example, in politics, a powerful person can often help his cronies or supporters get preferential treatment or protection; In business, large companies can use their own strength and resources to make it difficult for competitors to gain a foothold, and it is easier for them to gain market share and income.