What is the origin of the idiom "chip on one's shoulder" and when to use it?

The origin of the idiom "chip on one's shoulder" is not entirely clear, but it is thought to have originated in the United States in the 19th century. It likely derives from the practice of placing a small piece of wood or a "chip" on one's shoulder as a challenge. In this context, if someone knocked the chip off another person's shoulder, it would provoke a fight. This expression often implies that the person is touchy or quick to take offense, as if they are challenging others to provoke them by knocking off the metaphorical "chip" from their shoulder.