When the ancients wrote calligraphy, they often wrote "attacking the clumsy" in the inscription. What does this mean?

Is it "careless work"? For example, Liao's "Shuang Qing Ci Cao": "Several poems are confined to poor and boring works, so as to get rid of the puppet in the chest, and the works are clumsy."

It means "poor handwriting, some neat and some clumsy, please don't care", which is a modest word.