If you are the partner who would really like to have more children, while your other half doesn't, you might resent him or wonder how you can persuade him to have more kids. Your partner may feel you are pushing all the time, and does not understand why you want to change what he (or she!) sees as an already perfect family unit.
The first thing you should probably do is considering your reasons for having the feelings that you do. Why do you so much want another baby? What are your partner's reasons for not wanting any more kids? Sometimes, after a lot of soul searching and talking, you will come round to your partner's point of view, or vice versa.
Feelings are not rational though, and there is no right or wrong. But if you cannot agree with your partner and you want radically different things, that definitely causes a lot of friction. For some couples, counseling is a good option. Sometimes, the partner that wants another baby comes to accept the other partner's wishes, and sometimes the reverse is true. Then there are couples who end up pregnant, even if they were not planning to. In some cases, disagreements over whether to have more babies or not leads to couples splitting up. Before that happens, it is a good idea to take the interests of existing children into account. Also see things every couple should talk about before trying to conceive, and getting your partner involved in pregnancy.