Why is it "forgetfulness", not "forgetfulness"

From the sixty-seventh chapter of Cao Qingxue Qin's Dream of Red Mansions: "As the saying goes,' the rammer flies first', which saves a moment of carelessness and makes people laugh." Story: In the play, Liu Xianglian saved Xue Pan's life and they became brothers. Jia Lian betrothed You Sanjie to Liu Xianglian. Liu Xianglian heard that You Sanjie was having an affair with her brother-in-law, Jia Zhen, and asked for the dissolution of the engagement. You Sanjie died a martyr, and Liu Xianglian became a monk. Xue Pan sent someone to look for it, but he didn't find it. Aunt Xue said that as long as there is movement, it is enough not to make people laugh. I wish you all the best, health, happiness and happiness. Please adopt it. Thank you.