What is the origin of the word "brag"?

"Bragging" and "bragging" are the most common mantras in people's lives.

When the traffic is not very developed, it is said that it is difficult to sail in the upper reaches of the Yellow River. To this end, locals often use cattle and sheepskin to make rafts to cross the river. It is composed of several cowhide bags shaped like bags. Blow up the raft with your mouth when you use it, so there was a saying "brag" at that time. You can't blow a raft without enough strength and empty talk. People often say to people who can only talk empty words: Go to the river to brag if you have the ability. Since then, people have called those who have neither knowledge nor working ability, who love to talk empty words and exaggerate.