What is the origin of the idiom "flash in the pan" and when to use it?

The idiom "flash in the pan" originated from the world of firearms. In early flintlock firearms, there was a small pan that held the priming powder. When the trigger was pulled, the flint struck the steel, creating a spark to ignite the priming powder in the pan, which, in turn, would ignite the main charge in the barrel. Occasionally, the priming powder would ignite in the pan but fail to fire the main charge, resulting in a flash without a shot. This was considered a failure, and the term "flash in the pan" emerged as a way to describe something that initially shows great promise or success but ultimately fails to deliver, often because it lacks staying power or substance.