flash in the pan

someone who experiences temporary success or achievement but ultimately fails to maintain it in the long term

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.

He was a flash in the pan in the music industry, with one hit song that quickly faded into obscurity.
The actor had a brief moment of fame after a hit movie, but he turned out to be a flash in the pan, unable to replicate his success.
The entrepreneur's business was a flash in the pan, as it went bankrupt shortly after a brief period of profitability.
She may have won that one tournament, but her career as a professional golfer was just a flash in the pan.
The athlete had a spectacular season, but critics thought he might be a flash in the pan, and his performance declined in the following years.

a sudden but brief success that is not sustained

The phrase "flash in the pan" originated from a type of gun, called a flintlock, in the 17th century. The gun had a small compartment that held a material that would ignite and create a flash of light when the gun was fired. However, sometimes this material would not ignite the main charge of the gun, resulting in no shot being fired. The metaphor of the flash of light without any real action can be applied to many situations where something looks impressive or successful but ultimately fails to achieve anything meaningful or lasting.

The new tech startup seemed like a sure thing, but it turned out to be a flash in the pan.It went bankrupt within a year.
The politician's campaign was the flash in the pan that taught them the importance of building a strong base of support over time.
His debut novel was a flash in the pan — praised briefly, then forgotten.
The startup's viral app turned out to be a flash in the pan, fading within months.
The band's chart-topping single was just a flash in the pan.