Flash in the Pan
Meaning
Something that shows great promise, then disappoints by being over too quickly.
Example
Joe Clark’s political career turned out to be a flash in the pan.
Origin
Flintlock muskets have small pans to hold the gunpowder fuse. Sometimes the gunpowder in the pan would flare up without firing the gun. That would be a flash in the pan.
Alternative: Derives from the early gold prospectors who would literally see a flash of light as they panned for gold, but who would often fail to find the nuggets on closer inspection.
