You're on the money. That's the honesty, openness, and communication part. If someone isn't honest with themselves and is opening the relationship without being able to compartmentalize sex and intimacy, then it doesn't work.
I think you're mixing things up, but I understand the gist.
You don't have to be in a monogamous relationship first, in order to have a successful open relationship. You aren't really managing a third person (unless you want to start discussing throuples). But what you say about honest and open is spot on. That's the first step, and probably the hardest step, in every relationship.
I often joke with people that the best thing for me, and my relationship with my husband, is when he started working for an airline. His being away 3 weeks at a time forced us to give up all of the mind games and be real with each other... very quickly. If we weren't honest with each other, our relationship wouldn't work.
But it also meant that we had to be very honest with ourselves. I couldn't take 2 days to figure out what I was feeling or be passive-aggressive. 2 days was 20% of our time together. So, if I felt annoyed, or bothered by something, I was forced to self-evaluate it, face it squarely, be honest with myself about how I really felt, and then accept it and just tell him or confront him about it.
We both grew up very fast during the year he worked for that airline. And, ten years later, we're both better for it.