Why do some people get married VERY young, like age 20, it makes no sense to me?

Some people make decisions on the strong, exciting immature feelings of love they experience in a relationship and expect these strong feelings to continue. However, what they do not realise is that these feelings cannot be sustained because cirstances change and the excitement wears off because they become acstomed to the person. Their expectations do not match reality and as such they become disillusioned and divorce. Successful young relationships are those in which people's expectations change over time.