When you break up from a poly relationship, you may continue to date (the sex is great).
As time goes on you consider restarting that great relationship you had and you say (in the heat of passion): “why can’t you [change something] for me?” As an example, consider this: “why can’t you go mono for me?”. And then she’ll say: “why can’t you go poly for me?”
Once many get a taste of poly, there’s no going back to mono. Yes, mono’s great with the right one, but think of all the hot dates you’ll miss.
If you have different relationship goals with your partner there will be that awkward moment when you don’t say more because you’ll ruin a great date.
For a journal of a Solo’s experience with her mono partner, check this link: https://tinyurl.com/2p8ukrth