Well, all forms of marriage, including collaring, take a good deal of work and commitment on both parties. It means accepting that you will not get everything you want out of the relationship. Modern Americans are taught to expect an almost impossibly high degree of satisfaction from marriage: your spouse is supposed to be your best friend, your confident, your perfect lover, a great parent, and to balance work and the relationship perfectly, and this is all supposed to just happen. That's just unrealistic, but far too many people go into it not realizing that no real marriage can live up to the Hollywood fantasy.
I don't have any experience with collaring, but I can imagine that it brings along some added pitfalls. Subs may not realize how much autonomy they are surrendering and doms may imagine that they get to have everything they want because they're in charge. Either of these attitudes can, I would expect, lead to problems with compromising. Even doms have to be able to compromise in long-term relationships.
