In my experience, both personal and professional this is true. Couplehood can make us to examine our faults because there is a lot at stake. But is knowing oneself a prerequisite for a good marriage? Of course a publication called the Philosopher's Mail thinks so. Me, not so much.
What follows from this smart, though pessimistic, view of human nature and relationships -- that a battery of psychological testing prior to marriage will enhance self-knowledge and knowledge of the other person and thereby fix what ails marriages -- is a mistake. A whopper of a mistake. A mistake on the order of picking a life-partner with eight strands of hair and no nostrils.
The mistake is that it both underestimates and overestimates what psychology is.
I recently saw a couple who had been married for 25 years in which the man was completely resistant to all my psychological blandishments, he wasn't hostile or 'in denial' or 'defended'; he just was completely uninterested in his own motivations. As he saw it, over the course of a long marriage, he had forgotten to treat his wife well and now he wanted a chance to do what she was asking for; more attention, more romance, more sex. I wanted to know 'why' but after three sessions he had changed and she was happy. The surgery was a disaster but the patient not only survived but felt much better. The lesson: Who cares 'why' if a relationship works? There are plenty of couples who are happy enough, for enough of the time that they don't need to spend a lot of time reflecting on it. (This is one of the great discoveries of John Gottman's research). It is easy to extrapolate from unhappy couples in a therapist's office to assume that all couples are unhappy. The dubious statistic (Philosopher's Mail, thankfully does not) about 50% failed marriages can re-enforce this idea (for why the statistic needs to be taken with a grain of salt see here). Even if we grant it for a moment that 50% of marriages will last sixty years, it is worth noting that the vast majority do so without without anybody ever stepping into a shrink's office. As I have remarked before, marriages, like people, are resilient. A realistically optimistic focus on individual and couple resiliency is honest and healthy.
The most serious problems people encounter in couples are not magnifications of the same problems they encounter in friendships or the work place. The reason for that is that a couple relationship isn't the same as other relationships. I see a lot of young couples, couples who have recently moved in together after a year or two of dating. They fight, they hurt. They come in bewildered because what they are experiencing is so different from what happens in the rest of their lives and what happened for the first year of their relationship.
From what I have seen, after a year or two in a relationship, if and when we feel safe with our partners people sometimes do something different than they do in other relationships such as friendships. My metaphor for this is: we come to our partner timidly, expectantly, filled with hope and reach out to them and offer them a beautiful silver platter filled with our shit. When we feel safe and loved and secure enough we bring out things that we haven't paid attention to or thought about or reflected on for years, things that we are ashamed of, afraid of, mistrustful of, don't have any idea how to handle. It is a paradox that the tribute of love is our own least loved parts. These are things that psychological testing won't discover. And our partner's reaction to us offering up our damaged bits can't be easily predicted.
Couples can and should talk about their expectations: money, career, housework, children, sex. People need to be honest with themselves about what is important in a partner but also need to know that will change over time.
I don't believe in compatibility so much as I believe in kindness, flexibility and positivity. Those qualities will see couples over a lot of hard stuff including a lot of incompatibility.