People mature at different rates, and those who are in a relationship might find it is a source of great frustration. Couples might find that one of them is ready to start a family, but the other person feels they are not ready to make that commitment. They see children as a trap that will keep them from accomplishing their goals, so they put off their partner. It might seem like a good idea to wait, but eventually the person who wants a family might decide to end the relationship rather than waiting.
For this type of relationship, it is often a case of their timing being off. One person is ready to forge ahead to the future, and they are willing to take the risks associated with it. They feel their relationship is stable enough to weather the bumps in the road that will come with this commitment, and they believe their partner is able to take the journey with them. A partner who refuses their journey might be mature in many ways, but the failure to agree to start a family is a sign they are not ready to shoulder the burden.
When the timing is off just a little, most relationships will continue. If there is a large timing gap, one partner will generally make the break to find someone else. It is generally based on how important their goals are, and a partner who disappoints them may be seen as someone who is not fully committed to growing through life together.
When it comes to major issues in a relationship, timing can be one of the most important factors between two people. Forging ahead in life is difficult, and waiting for a reluctant partner to move is often seen as a failure. There are those who will wait, but it often depends upon how much time they are willing to give before the relationship breaks down.