If I had to name just one quality, it would be “TIME.”
That may sound like a strange answer but it's true. I remember a not-so-kind member of the family telling me, “You and your husband spend too much time together!” I couldn't believe what I heard. I responded, “Isn't that the point of marriage?”
Surprisingly, it's not a popular answer! This person you married, married you. While it's not always easy to spend time together, it's necessary. When you devote one of the most popular commodities to someone, they feel wanted, appreciated, loved and when you're together, you get to know each other in a more real, intimate way.
When you really know someone, eventually if you're honest with each other, you will learn about the sensitivities of each other, what makes each other tick, and most likely, they will learn weaknesses as well. That's not such a bad thing! When someone loves you and sees your weaknesses, then they will know how to help you and you will learn how to help them. It's an adhoc way to learn about someone - just lock a couple in a room and good or bad, they will come out knowing each other on a much closer level.
It's not a business agreement…it's marriage.