The Orchot Tzaddikim has a chapter all about קנאה, jealousy. It speaks about how detrimental it is for an individual who possesses this horrible negative character trait.
A person who becomes obsessed with another, and wishes negative things will happen to them. The jealous person becomes a miserable person. He knows no happiness, because he does not know how to appreciate what he has.
There is an element of lack of faith with such a person. It’s as if he is telling Hashem that He made a mistake with how He has taken care of him. If he would have received more wealth and success, like the person he is obsessed with, he would not need to be jealous.
The remedy to overcome jealousy is to truly learn how to feel happy with what he has. He should feel humbled by G-d’s generosity in giving him all that he needs.
An even more effective remedy is to learn how to genuinely be happy at another person’s good fortune. When something good happens to a friend, or he celebrates a family Simcha, learn how to be sincerely happy for them. This is greatly lacking in the world today.
Only a person who is not jealous and feels good about himself, is able to feel another’s joy, and really feel what he is feeling. One who can do this will find great peace of mind. This shows good character.
This needs to be shouted out. Be genuinely happy at someone else’s good fortune, and most importantly, stop being jealous!