We feel it because we want what someone else has but we are taught to just not feel it, so most of us just identify it as something else, pity is an easy go to. You are jealous of that friend with a big house and great job but really you just pity her for working so much and not being happy with a simple life, she is vain and needs material things to be happy, poor girl. No, not true, you are jealous and you are jealous because you want that too.