Marriage is a sacred union of two persons in love with each other. They should know the responsibilities and problems that they may encounter. They should be ready on the things that they will come across. .
As for the case of teenage marriages, considering that the couple is young, they may not know what they are going into. Some may still be immature - not being aware that marriage life is not as easy as one, two, and three. Once they are married, their gimmicks and night outs will be limited. These and other petty things may possibly cause friction. And as a result, their marriage will be a disappointment.
In some circumstances, teenage marriages are caused by unwanted pregnancy. They are just forced to marry each other but the girl may not really love the boy (or vice-versa) or the couple isn't ready to enter marriage. Marrying someone that you do not love is such a wrong thing to do. That's why teenage marriages are not always a success.
Financial stability is another problem. Typical case is when the couple can't find a job because they did not finish their studies. And because of economic crisis nowadays, the couple may not survive in financing their basic needs. It will be really hard for them to find money and cope up with today's changes.
Another problem of teenage marriage is relationship with in-laws. For example, the parents of a girl may not like the boy for her because of his status in life. So the girl got to choose between the boy and her parents. When she decided to choose the boy, her parents might have bad attitude towards her husband. Such incidence may lead to separation.
Not fully knowing your partner's personality is a disadvantage too. To illustrate this, a girl and a boy know each other for weeks - they started out as friends, go out on a date, become steady, and then because they thought that they"re really love each other, they decided to get married. Only to find out later that the boy has many vices, irresponsible and reckless.