Have you heard of the two following messages in open literature?
1. Never open up a relationship that has "problems" or "issues," or that you consider rocky. Opening up a rocky monogamous relationship is a recipe for disaster.
2. One person cannot satisfy 100% of your relationship needs/wants/desires, or vice versa.
J and I have been discussing how to square these two messages. I think it's about how you define "relationship issues" and your attitude toward them. If your issue is that you don't communicate effectively or that feelings of dependency or possessiveness keep you from experiencing other relationships, perhaps that should be worked on and addressed before adding more people to your relationship. Similarly, if both individuals have not spent any time time working themselves (learning to manage jealousy, finding different ways of communicating or relating, etc) this should probably be done before those individuals can expect to make another simultaneous romantic relationship work. However, if your issue is that one partner is really into BDSM related activities or tantra or anal sex or has a foot fetish and the other one isn't, then maybe that isn't an "issue," but rather an incompatibility that can be resolved by seeking another relationship that can satisfy that need or desire. (A parallel idea here would be to think about non sex or romantic activities. If one person is really into scuba diving, knitting, or talking about politics and the other isn't, it is quite natural and healthy to explore and enjoy those activities by oneself or with other people. We would probably consider a relationship to be unhealthy if one partner kept the other from exploring those things because of deeper issues.) More importantly, though, I think is the recognition that perhaps opening up a tumultuous monogamous relationship is not a great idea, but experiencing challenges within an already open relationship and then using that structure to your advantage to move through challenges makes a whole lot of sense.
I don't think these two messages are necessarily at odds with each other. I think they can be major difficulties if one partner's desire is to have a need met exclusively by the one partner who is simply not interested in whatever activity it is (for example, if one partner has a strong desire for anal sex and is only interested in doing that with their primary partner, and yet their primary partner is not interested in anal sex). I think, too, if one partner approaches this "issue" as a relationship deficiency rather than a simple incompatibility, then it starts to create difficulties in squaring those two messages. If one partner is genuinely unhappy with their relationship because a particular need is not met by that relationship, then it probably won't suffice to have that need met elsewhere, and it may be that that partner needs to find a different partner where that need is met within the relationship. (For example: Perhaps a couple is having challenges because one person really wants to explore D/S and the other is not interested, or has tried it and decided that it's not for them. Is this relationship considered "rocky"? How does each individual think of this challenge? How is it framed? Is it necessary for the D/S relationship to be part of their relationship, or can the one person who wants to explore the D/S relationship fulfill this need with another interested partner?)
So, I think it has as much to do with the framing of the "issue" and the individuals' approaches toward it as it does with the "issue" itself.
Lastly, I think that first message is pretty interesting because it is couched within a monogamy framework. It assumes that all healthy open relationships come from healthy monogamous ones. I think there is some merit to allowing two people to come together and build trust and honesty and to create a shared history together. And, a relationship should have healthy characteristics: good communication, healthy emotional and practical boundaries, honesty, trust, respect, consent, etc. But starting off a relationship as open to avoid issues I don't think is necessarily a bad idea if the people involved are happy with that decision and it makes sense based on the individuals' needs and desires.