The problem is people often change in fundamental ways. It is difficult to choose a partner in your early 20s who will retain the same value system throughout

The problem is people often change in fundamental ways. It is difficult to choose a partner in your early 20s who will retain the same value system throughout their life. Both myself and my ex are very different people from what we were in our 20s. There are many factors that contribute to a successful marriage. I'd say commitment is one - you have to want the marriage to work. You have to accept that the other person is an individual and accept that they aren't your twin and also that they are free to grow. You may disagree, for instance politically, yet you have to respect them and allow the differences. It's tough to run a 3 legged race for 30-40 years.