Ego Between Couples
A marriage that ends up in a divorce is mostly not caused by one incident; it is usually as a result of the accumulation of several minor and major unresolved marital disputes. If these minor and major marital disagreements had been effectively taken care of when they occurred, then that destroyed marital union would not have hit the rocks.
Most people are used to living a single life, where all they think about is self. This is probably one reason why once they have a relationship or get married, they tend to become selfish and think only about their own good.