A band or singer that everyone forgets about after their hit song runs its natural course into
obscurity, because they can never get back onto the charts again. Most one-hit-wonders are that way because either they can't write their own songs, or their own songs are crap.
Crossover songs and artists are sometimes mistaken for One-Hit-Wonders, because listeners outside their genre don't know who they are. Anyone unfortunate enough to make this mistake is likely to be taken to task by numerous members of the artist's following, because it takes quite a good artist to pull off a
crossover hit.