said that Qu Qiubai was Lu Xun's "bosom friend" for two reasons.

firstly, Lu Xun wrote more than 1,3 letters to others in his life, and only one of them called him "comrade", that is, Qu Qiubai.

Secondly, after reading the Selected Works of Lu Xun's Miscellaneous Feelings compiled by Qu Qiubai and its preface, Lu Xun wrote a banner and gave it to Qu Qiubai: "It is enough to have a bosom friend in life, and the world should treat it with the same bosom." It means that a person only needs to have a true friend who fully understands himself in his life. This shows that in the midst of difficulties and hardships, the deep ties between two people have been firmly linked, and they are soul mates and help each other in times of trouble.