Unnecessary jealousy

By "unnecessary jealousy" I automatically imply that there is 'necessary jealousy'. Not sure if I mean it that way, but I do think that jealousy is inevitable in some situations and it is how we deal with it that makes a difference.
There can be reasons to be jealous, and when we are it is hard to rationalize and put things into perspective. Therefore the situation heats up and we become very uncomfortable, and I personally believe that it is the state of angst that drives it. Angst, being scared of what we cannot define as opposed to fear that is definable yet threatening. Therein also lies the difference between two types of jealousy. The forbidden one - the angst related jealousy, and the reasonable one - the fear related one.
That being said, I believe that regardless of signs and natal charts we as people should still consider what we put each other through. I know people who like to make each other jealous because it's entertaining and exciting to have caused that emotion in someone else, and I've also been on the receiving end off that. My gf mentioned that she sometimes finds it 'cute' or 'attractive' when a guy is a little jealous. I objected to this asking her why she would want induce that in another person. Had she not been jealous before thus knowing how agonizing it can turn out to be? She had, I just don't think she, or anyone who takes pleasure in it, have considered the consequence by reversing the situation.

Thoughts...?

The only reason there is ever jealousy is because it comes from thinking you own something.

"The only reason there is ever jealousy is because it comes from thinking you own something"

That may very well be in some cases, but also I believe that we all have deep layers that only we, ourselves know about, and that's where we store information about our true intentions. These may be pure and rational to our selves, but they don't have to be. But it's when we act on them that we may end up hurting someone else, and not because they feel they own us, but because they invested trust in us and are hurt when that is broken.

...yes?

But what I'm really talking about is: what is jealousy to you (people in general, but certainly also you sag89)...? And why do some people like to play games with jealousy? Is that the only way to find out if a person really likes you?