When I tell people who don't already identify as poly about choosing this for myself, one of the usual responses is that this won't be a successful relationship model. After all, if over half of traditional marriages end in divorce, how can something that is more complex survive?
This viewpoint is based on a pass-fail way of looking at things. If you do a relationship "right", you'll be together, forever, until you die, and anything else is a failure. To that, I say: Crapola! Each and every relationship I've ever had, including the ones that would be considered failures by this measure, has taught me new skills, brought fresh perspectives, more awareness, and a more developed sense of self.
Relationships are often about learning things from others that you might not stumble across on your own, so even when it isn't something that lasts forever, there's still value in what is learned, and from what is taught in return. Some of those lessons aren't as easily accessible in a day-in, day-out relationship, others seem to require a level of consistent exposure that scours away artifice, where routine becomes a path to deeper understanding of self and other. Some of the things learned show us paths that aren't desirable, others grow even more enriching upon repetition.
Having been in a space where the dissolution of my marriage was a distinct possibility over the past several months, I've thought about that whole pass-fail dynamic a bit. I'm very happy that the reset button has been hit, and things are on a positive track, but even in the darkest time I wouldn't have seen a divorce as a failure in the sense that most would. I've been blessed to be in a wonderful relationship with a caring and supportive partner since I was 18 years of age. If it had ended or changed significantly, that wouldn't have changed. There are a great many ways that having a stable connection for my entire adult life has been beneficial, and that value doesn't just go away.
That said, one main thing I seek in a relationship is continuity, so it's something that I select for with partners. I'd rather have good long-term relationships than something fleeting, no matter how intense. The difference is that, if things don't work out as planned, it isn't a failure. It's an opportunity to learn and do better the next time. It's only if you stop trying, allow the fear of failure to limit your opportunities to love, that failure becomes part of the equation.