One of the worst twists a relationship can take is when one partner abuses the other physically or verbally. Nobody deserves treatment that ends in physical or mental harm, and when that happens, the best result is the end of marriage.
Old baggage from previous relationships can lead to complications in the marriage and cause you to be unsure how the partner views you. This can lead to unfair accusations, unattainable expectations and many other problems in a relationship.
In a marriage, one partner may need so much affirmation from the other person that he loses within his role in the relationship. This can lead to a partner taking his own abilities for granted or completely forgetting his personal needs.