People enter a relationship to be happy. It is expected to succeed. So often the opposite is the case. Many relationships end up breaking down, and for those that hold together do so without bringing anything like what was wished.
Of course realistic expectations are essential. Life isn't a fairy tale, nor is anyone perfect. But if we understand that, there is something I have found that gives a fine foundation to a relationship. That is the desire of both parties to put the other's happiness first. If that is done (and it isn't easy as we are, as already noted, not perfect), then good. However, putting the other first - from both sides - is a sound basis to living together with someone.
Part of doing that is taking turns yielding and doing what the other wanted for us. In that way mutual respect and love will flourish. That is true success in any relationship.