[B]What leads to Jealousy?
[/B]
In my opinion it is the competition with another fellow which leads to jealousy. Unless you have no competitor (in any field, love, education, profession, politics etc) you won't feel jealousy.
This jealousy is what eats up all your good qualities. It cause frustration. It strengthens your id and weakens the Super-ego (a control agent).
[B]Competition leads to Jealousy and Jealousy leads to Prejudice. [/B]
When you are in competition with someone, at first you try to be friend with him/her and you don't know that you are in competition with someone (all goes unconsciously). Later on this internal feeling of competition starts showing themselves in your conscious. Slowly and gradually this conscious feelings of competition causes you to feel jealous to your competitor. (continue).