What's in a theme song?

As my friends already know, I like to find theme song for my RP characters and sometimes theirs. But lately, I haven't been able to find a theme song for Juliet, my character over at Marvel. I've listened to my iPod and iTunes everyday with no success.

Question is, is it possible to find ONE theme song for a character? Just for Natasha I had to choose between many songs that fitted her. In the case of Juliet, there's one song that would have worked if it wasn't for the beginning of the song.

Anyway, I did on Facebook a meme where you were doing the soundtrack of your life if it was a movie... 'course you had to put iTunes on shuffle. So the result was very random. Thing is, that meme made me realize that not just ONE song can define a character or a real person. One song can represent a mere moment of our life. 

Strangely, I did found one theme song that goes to all my characters, who are all based on me.