People can get jealous for several reasons. But the motive is always the same: greed. Yes, jealousy in envying what another had got and you do not.
Now this can occur in every situation, even in a family, or among best friends.
How can those things happen? Well, when two colleagues are on the same job, in the same office and get along fine, one suddenly get promoted, gets a bigger working space and a better pay, the other might get jealous.
There is always this question involved: why him or her and not me?
All your friends are in a relationship and you are still single. That might not always be nice to cope with. This one you really liked, also picked somebody else?
Why does this person has a bigger car, more money?
Yes, jealous people do question themselves, but in a different perspective. Yes, deep down they might be happy for the other party, but sometimes they only feel their own lack.
This is what causes jealousy: inequality.
There is not much you can do about it. Life is not fair and the world is not a all prefect. So yes, when you are in a certain position people look up at you, there will be some jealous.
Also on writing sites this might occur, like here on Helium, when one article outranks yours.
Yes, you can get an attitude, get mad because that writer might earn more, but you can also keep in mind that this writer might have worked better than you, or that the others simply like his or her article more.
Sometimes there is not reason why things are unfair. You cannot make up the mind of another.
We all get jealous somewhere in our lives and it is not a shame to be. Yes, we all like to be winners, but this is something you cannot always be. Sometimes others also like their glory.
Now here is when jealousy can become dangerous: if you let it control you. Most likely we have all insulted somebody, got rude or even vandalized things because of jealousy.
Sometimes frustration gets that high, it takes the best of you. When this happens, realize you are on the wrong track and that you might need help.
Nobody is the center of the universe. Not you and not the person you are jealous about. Talk things out and find out that this person you envy, might envy you as well.
For example: you are poor and unemployed and look up at those with the cash and the high positions, while they might like to have some of your free time. Yes, some might work extremely hard for what they got. Only few rich heirs might be lucky to get it and still, they have the task to maintain it.
Thinking of all that: jealousy is a normal reaction. We all have it. But most control it and do not give in to it.