Why people wants more and more likes and comments on their post on facebook , i want to understand the psychology behind it ?.
Well, probably it is just another new way of addiction. I mean: in this abstract world, relationships are now working as a kind of pathological-video-game, where everybody needs public recognition in order to feed their ego. Many people have fallen in the "like" trap, as the only way of looking at themselves as someone "successful". The problem behind that is precisely what this "success" implies: a fallacy. There is no real success behind a screen, but on every single act, you do in your life. So, maybe, to be hidden behind the likes you receive every single day is just another way of running from your personal frustrations.
Now, this "cyberlife" can also be seen as a way of control. However it can be looked like just an entertainment, or, as many people claim: " a way of communication", or "a tool", I think this is far more complicated than this: if you convince the people to share everything they do, probably you have all the power you need in your hands: sensible information. Facebook, many times, has been accused of using algorithms to get the people depressed, for instance. Why? because it is better for any business to maintain the people depressed, they will buy whatever shit you offer just with the hope of feeling better.
So... the psychology behind the like, and coming back to your central question, is an addiction, I think. Facebook is working as a new and great necessity for people to feel recognized, to feel a part of something, and, at the same time, it is being used to manipulate the people into a new way of thinking, into a new way of necessity, of shopping, of having a single opinion. It is just the perfect "social mind shaper", and a huge addiction.