Jealousy can be helpful as well as hurtful
If it is intense, it may sour his outlook on life for quite a while. But jealousy is one of the facts of life and can't be completely prevented, so parents shouldn't expect to accomplish the impossible. However, they can do a great deal to minimize it and to help the child convert it into other feelings that are painless and constructive. If he comes to realize that there is no reason to be so fearful of a rival, it strengthens his character so that he will be better able to cope with rivalry situations later in life, at work, and at home.