This is a hard question. But I think having a successful relationship is about having a real plan for the future together, and both people having the means and motivation to contribute to and realize that plan. This gives a relationship purpose.
Whether you're talking about Western-style dating or a purely arranged marriage, when people allow themselves to simply fall into a relationship because it's convenient, it's what their parents want, etc., often have a harder time finding that purpose in their relationship. Factors like children, religious faith, etc., can force a purpose, but I think when the mentality that 'we have a mission together in life, and this is how we're going to accomplish it' is missing, a relationship can feel very empty regardless of whether the couple stays together or not.
What do you mean by real plan for the future?