“Jealousy is born out of comparison”. And we have been taught to compare, we have been conditioned to compare, always compare. Somebody else has a better house, somebody else has a more beautiful body, somebody else has more money, somebody else has a more charismatic personality. Compare, go on comparing yourself with everybody else you pass by, and great jealousy will be the outcome; it is the by-product of the conditioning for comparison.
Otherwise, if you drop comparing, jealousy disappears. Then you simply know you are you, and you are nobody else, and there is no need. It is good that you don’t compare yourself with trees, otherwise you will start feeling very jealous: why are you not green? It is better that you don’t compare with birds, with rivers, with mountains; otherwise you will suffer. You only compare with human beings, because you have been conditioned to compare only with human beings; you don’t compare with peacocks and with parrots. Otherwise, your jealousy would be more and more: you would be so burdened by jealousy that you would not be able to live at all.
Comparison is a very foolosh attitude, because each person is unique and incomparable. Once this understanding settles in you, jealousy disappears. Each is unique and incomparable. You are just yourself: nobody has ever been like you, and nobody will ever be like you. And you need not be like anybody else, either. Everybody seems to be so happy - except yourself. You are continuously comparing. And the same is the case with the others, they are comparing too. Maybe they think the grass in your lawn is greener — it always looks greener from the distance... Everybody is jealous of everyone else. And out of jealousy we create such hell, and out of jealousy we become very mean. If everyone is in misery, it feels good; if everyone is losing; it feels good. If everyone is happy and succeding, it tastes very bitter.
But why does the idea of the other enter in your head in the first place? because you have not allowed your own juices to flow; you have not allowed your own blissfulness to grow, you have not allowed your own being to bloom. Hence you feel empty inside, and you look at everybody outside because only the outside can be seen.
Source: The Book of Wisdom.