Also remember that this never happens:
"Suddenly, the heavens open and a beam of light shines down from Heaven as the Angels are up there, singing to you the Perfect Song, so that all you have to do now is to record it [and retire]."
Don't "keep starting over," because if you do, you won't "do" anything. Instead, keep every version of everything that you write, and don't be afraid to let someone else hear it. (Especially in a safe place like "right here.") But also, don't find yourself "craving 'affirmation.'" When a song sounds good to you, it is good.
"Creativity is not deterministic." There is no "right answer." A song is never truly "finished." And a significant part of the process is – frankly – "trial and error." Or maybe just "trial." "Experimentation." The person who finally hears "the song that you decided to release" never hears, and probably never suspects, all of the stuff that you didn't decide to include. "To them, it simply sounds 'inevitable.'" The decision-making can't be seen ... and you probably should prefer it to be that way. (Just tell 'em that it's magic ...)
But to this I would add one more thought: "don't 'discard' anything." What didn't work on this one might be perfect for the next one. Newspapers used to keep what they called "the morgue," where they kept the stuff that they didn't use. Because, every now and then, they'd go back to it and find exactly what they [now ...] needed.