The five star rating

How do you decide if a song is worth the legendary five star rating on Itunes? I'd like some thoughts on this. My mind has been troubled with this since I started using computer media players with the rating option. The five star rating indicates that the song is in rarified air, that it is the best of the best. Too often I toss out a five star rating to a song that doesn't deserve it and feel regret later, as if I've betrayed myself. My new attitude is that if the song comes up on shuffle and I want to skip it, then it's no five star song. It's my only way of performing quality control.