I don't know but here is what Melody Beattie had to say about it in her book 'Codependent No More'
Two codependents in a relationship can really play havoc with each other. Consider two people-pleasers in a relationship with each other. Now consider two people-pleasers in a relationship with each other when they both want out of the relationship. They will, as Earnie Larson says, do horrible things. They'll nearly destroy each other and themselves before one will stop rescuing and say, "I want out."
I believe it.
I need to read that book again. While I can see progress in myself and can identify areas I need to think about first, and make better decisions, I am still totally amazed when I interact with people that are NOT codependent. Now that I am paying attention it is fundamentally very different.