I'll first couch this by saying I'm not poly, I am monogamous.

I don't see why an open relationship would be anymore "doomed" to failure than any other kind of relationship - monogamous, hetero, homosexual, etc. From my relationship experience it really has to do with how honest each person is - both with themselves and with their partner.

If one of you is doing something they don't really want to do, just because they think it's what the other person wants... that is unlikely to last long in my opinion. But if it is truly what both partners want, and both partners are willing to set ground rules, boundaries, and declare their expectations - and then both partners are will to live by those honestly - then why wouldn't it work? That's what relationships are about, and no 2 relationships are ever exactly alike.

Relationships also grow and morph over time, as do people. As long as both partners grow and morph in the same general direction, and keep the lines of communication open, the relationship can grow and morph in healthy directions - rather than crumble. In fact, some relationships begin as closed or open, and then eventually morph into the opposite. As people find what makes them happy, communicate about it honestly, and work to change together rather than grow apart.

If someone is just going along with the other person just to avoid rocking the boat, that type of relationship is unlikely to last. (Whether it's open, closed, hetero or homosexual.)

Just my 2 cents.