Having been through two divorces, I'd say the biggest problem is substantially different values. When one wants to live simply, save for the future, keep within a budget, but the other is spend it as fast if not faster than we get it, no financial self control, big problem. If you can't conceive naturally, do you accept it, try to adopt, or spend tens of thousands on IVF? Where do you draw the line with in laws and relatives who make demands of your time, money, offer unsolicited advice? How do you resolve religious differences and what if one of you wants to change paths? Too many people are in a rush to get married instead of thinking of these things which if they become sources of conflict will destroy a marriage.