Explanations and sources are different.

1. Different explanations: Useless meaning: no value at all, no use at all. To no avail means that there is no help or benefit to the matter, and it means that the problem cannot be solved.

2. The words have different origins: None of them are from the 81st chapter of Cao Xueqin's "Dream of Red Mansions". To no avail comes from "Shuo Yue Quan Zhuan" written by Qian Cai of the Qing Dynasty: "Don't I know that the bandits and soldiers are strong, so I take you with them, but it will not help. Difference refers to the difference between two or more things.