a flash in the pan .昙花一现，转瞬即逝，多用来形容某事“持续时间短”。

 flash指“闪光”，pan指“旧式枪的火药池”。a flash in the pan指“火药在药池点燃后所发出的闪光”，一般用来形容某事“持续时间极短暂”。比如：
        He used to be called a young entrepreneur. But soon he was forgotten by the public. He was a flash in the pan.
        他曾被誉为青年企业家。但不久就被公众所遗忘。他真是昙花一现啊。
        Don’t count him in. You know him. His determination is always a flash in the pan.
        别把他算进去。你还不了解他吗。他的决心持续不了三分钟。