Envy is a natural emotion. It is the emotion that makes a five-year-old wish he could reach the doorknob the way his sister can—or ride that bike. Envy is the natural emotion that makes you want to do it again; to try harder; to continue striving until you succeed. It is very healthy to be envious, very natural.
When children are allowed to express their envy, they bring a very healthy attitude about it to their adult years, and therefore usually move through their envy very quickly.
Children who are made to feel that envy is not okay—that it is wrong to express it, and, in fact, that they shouldn't even experience it—will have a difficult time appropriately dealing with their envy as adults.
Envy that is continually repressed becomes jealousy, a very unnatural emotion.
People have killed because of jealousy. Wars have started, nations have fallen.