Can an open, collaborative approach still work when not everyone has opted in?

Over the past two weeks, I've been reading the book Power and Love by Adam Kahane (thanks to Eugene Eric Kim for the recommendation). After working with Eugene on the story of Wikimedia's open strategic planning process, I'd remarked to him that the Wikimedia effort was one of the most successful, large-scale collaborative exercises I'd ever seen.

Eugene replied that if I thought their project was big, I should read Power and Love to get a sense for the types of large-scale collaborative projects Adam tackles, often on the scale of nations. It's really a wonderful, introspective book, filled not just with successes but failures as well, and is probably one of the better-reviewed books I've seen on Amazon...