In Greek mythology, Prometheus was punished for stealing the fire from the gods by being tied to a rock and having his liver eaten by an eagle, only to have it grow back overnight to be eaten again the next day. It's essentially a never ending cycle of punishment (though he was rescued at some point in the story IIRC).
But wouldn't "old liver, new eagles" make more sense? Or at least the same? It's still his liver (regrowing), and new birds feasting on it (because yesterday's birds might be still digesting you know). Or metaphorically, there's always new problems to make your life shit.