Defined as returning back favor done, commending one's accomplisments or achievements, a praise to something beautiful, awesome, unique, one of a kind, and any gesture positively given back is an Appreciation in a sense.

Those who appreciates, are not selfish, nor envious, nor jealous, carefree and do always have positive outlook in life.

As for those who do not, those are types who are greedy, who wants always an attention drawn only to him/her, or worst and sad reality, those who are maybe haven't experienced be complimented or appreciated back by people around him in their entire lives

Appreciating even a small good gestures or achievements done by a person can teach one to be thankful for all the things and people he has around him.