Why do we envy?

We are thinking or experiencing dissatisfaction in whatever we have or doing. The things, people, condition or actions we are doing now seem not to bring us happiness. This dissatisfaction and lack of contentment is actually making OUR existence miserable.
And we look at others as wow how come they are happy, contended and fulfilled and we are not. What do they have or doing? And so, we desire to have and get what they have assuming that once we get or do WHAT THEY HAVE OR DOING then we will be happy OR HAPPIER THAN THEM.