So Many 'Why's . . . :)

Why are we all so very mean with everyone we meet? Why is it that when you meet a person, you build a perception in your mind immediately about him/her? Why is it so that the perception is a highly variable term, say x? Our variable x varies either from good to bad or from bad to good. But my big question is, on what grounds does this value of x change!!?
For instance: You meet a person for the first time. Say, you kinda dislike him in those couple of first looks. You form a perception in your mind that you don’t really like him (or he isn’t worth your liking or whatever!) **Here you assume the person to be inferior to you in some way or the other. The ways could be their attitude towards life & people, maturity, intellect, ego, etc.**
Maybe you find that person not much important to be even noticed or given a thought over, by you! Maybe it’s not the case that you find them inferior, maybe you just don’t find them worth your thoughts or attention! Frankly, I don’t mind such an attitude towards others At All!! Live and let live!
However, this attitude changes dramatically when you get to know about some of their huge achievements or their popularity for that matter, their hidden talents which had not been revealed yet, or something that they have that’s certainly more than you!
Why!? Tell me why do we judge people as WE wish! For instance, there’s this guy, you met the other day, found him a mediocre, there’s nothing special in him as such and you preferred maintaining that formal distanced relation. Sometime later, you get to know he’s a highly talented guy with umpteen achievements in some field! Being a humble and modest guy, he never really made any attempts to display that side of him.
However, right after that day, you started talking to him (more), admiring him for his achievements and always trying to stay ‘connected’. Why so? When will people stop being mean and when will they stop believing that ‘it’s they who decide what the worth of the other person is’? OR maybe it’s true that ‘the rising sun gets all the salutes”!! Stay mediocre and nobody notices you, come up with some achievement publicity and they’ll all come after you!! Even those who didn’t seem to know you before!