What is Su Shi laughing at when Dan Er writes to him at night?

Su Shi's self-laughing in Dan Er Ye has two meanings:

1. Smiling at oneself can be understood as self-deprecation or self-ridicule. In "Dan'er Night Book", Su Shi was amused by his contradictory behavior. He was demoted to a remote place, but he still envied the activities such as "Good Moon, Big Book, and Singing" spread in the Central Plains Cultural Center. This kind of envy The contrast with who he is in the middle of nowhere makes it hilarious.

2. Erxiao Han Yu. Su Shi felt that although his situation was bleak, Han Yu was demoted to a more remote place, but he was still able to write works such as "Autumn Embrace Poems" to express his inner sadness, and he was just envious of the good moon, big books, and beautiful scenery in the Central Plains. Although the singing is desolate, it is not as desolate as Han Yu, so it can also be regarded as Su Shi's alternative "mockery" of Han Yu.

The above is my personal understanding and is for reference only.