Calvin
»Why would she want another kid? She's already got me!« calvin exclaimed with fear.
http://www.calvinandhobbes.com/ 1986/11/07
Calvin is pretty much left alone, he doesn’t get enough attention from his parents. Sometimes he acts as if he hated them. One would think he does.
But in fact he is waiting to be loved, accepted and understood. Probably he is not aware of it. But when he thinks they would have another child, he gets scared and upset. That would probably mean, that he would be getting even less attention and love, which he so much longs after.
If one is satisfied in certain relationship, which is important to him, if one feels appreciated and accepted enough, he does not have a problem and is not jealous or afraid. On the other hand if one feels significant lack of affection, especially if he is a child, and he knows not how to overcome the sensation of not being appreciated, he must separate his sensations from consciousness. Also older children or even adults often do so. But then, when confronted with a possibility of having even less, although they are not aware of the lack, they get anxious and scared, and they do not like the option.
The bottom line here is: if you suffered lack of attention or love (although you may not be aware of it), you easily get jealous and afraid when possible that you will get even less. And it is quite possible that you do not understand these feelings and that you even feel guilt about them. But they origin from your inner lack.
Check out these links for Dr. Arthur Janov theory about neurosis and the primal pain: