flash in the pan

noun2

1. •
   (figurative) A transient occurrence with no long-term impact.

   • The concept turned out to be merely a flash in the pan and is no longer used.
2. •
   (figurative) A career notable for early success that is not followed by any significant accomplishment.

   • He was named Best New Director of 1940, but his career was a flash in the pan.