How did the word brag come from in traditional culture?

There are three theories about the origin of bragging:

1. According to expert research, the word boasting originated in the upper reaches of the Yellow River. In order to solve the difficulty of crossing the river, the residents along the upper reaches of the river came up with a method of using rafts instead of boats, mainly because it takes very strong people to blow sheepskin bags, and cowhide bags are too big to blow with their mouths. If someone says they can blow them up, it will be considered bragging. After a long time, it will become bragging and spread slowly.

2. It is said that they come from nomadic people. When nomadic people get together, they will talk about cattle and horses and say how many there are. This is exaggeration, so it is bragging.

It is said that it comes from the butcher. After killing pigs and sheep, the butcher will blow up the skin, but the cowhide is not easy to blow up. If someone says he can blow, he will say he is bragging.