There is not much explanation for this, and more people use it, which also conveys a kind of motivation to express courage, not afraid of difficulties, forge ahead, strive for progress, and is also an emotional catharsis. Sending this is also to encourage the other party to be self-motivated, not afraid of all difficulties and go forward bravely.
Source:
The stem comes from the "brave" sound of an up subject. Among the top-ranked works at present, when the up owner chats with his friends, the friends encourage the up owner to send out an expression pack of "Brave Niu Niu is not afraid of difficulties".
In addition, he said with great momentum that "brave Niu Niu is not afraid of difficulties" to encourage Master up. After that, this sentence and this expression pack became popular on the Internet, and then various versions of "not afraid of difficulties" expression packs appeared. There are also various styles of Brave Niu Niu Not Afraid of Difficulties, and various styles of voice packages.