Every song falls short of the glory of what a song could be. That's why the urge is there to start again and yet again. Often it's the fault of rhyme. I've discovered a hundred times that there just aren't enough rhymes to say what I wanted to say, so I said something else instead. Sometimes it was a better thing, but the thing I meant to say went unsaid. So there's an opening for another song.
The entire vitality of art depends upon its being either full of truth, or full of use; and that, however pleasant, wonderful, or impressive it may be in itself, it must yet be of inferior kind, and tend to deeper inferiority, unless it has clearly one of these main objects, either to state a true thing, or to adorn a serviceable one.