Yes, times a million. I was poly before becoming involved with my most recent ex. I fell in head-over-heels love with her, and she wasn't comfortable with having a polyamorous relationship, so we started a monogamous one. I didn't have any other relationships at the time so no one got hurt.
Yes, it was hard. I had to learn how to not make her jealous and to not be so open with others. But we lasted about 3 years before, get this, SHE LEFT ME FOR SOMEONE ELSE! Had she been open to polyamory this could have worked out. But her jealousy and lies wouldn't have allowed us to continue either way. I think one of the best aspects of polyamory is the level of honesty and trust, and she just wasn't trustworthy with how secretive she was with this other woman. It's unfortunate.
Anyway, yes I do believe people who are polyamorous can be successful in monogamous relationships. I never cheated, but it did feel a little unnatural after awhile.