I think it's important to have somebody you trust to be straight with you, and tell you when something is not good enough.
If you are a composer and have a submission due, it is crucial for your trusted friend or relative to hear it, and give you honest feedback.
This way, a third person can judge your work, and you can move on from the there.
It's amazing how my music develops when I play works in progress for these people.
Percussive pieces become orchestral.
Ballads become groovier.
Lyrics always change.
Who do you trust enough to critique your music?