Psychologically, opposites cause divorces. The first thing you learn when it comes to training for finding a mate in psychology class is that common traits bring people together. It is ok if there are a few things that are different such as food likes, styles. However, the people have to meet in the middle to create a good couple.
They must have the basics the same though. Their beliefs, values, morals, etc. This is why eharmony.com does so well for couples.