The phrase "flash in the pan" refers to something that appears promising or successful at first, but then quickly fades away or fails. It is often used to describe a brief and unsuccessful attempt at achieving something, such as a new business venture or creative project that does not last long or turn out as planned. The phrase comes from the phenomenon of a spark or flame that flashes in the pan when it falls short of igniting the fuel completely, resulting in a brief and unsuccessful combustion.