So what is the whole deal about having to be different? Standing out from the crowd that everyone touts all the time. Does it make sense? Well, diversity can perhaps take one to Harvard - like in the movie Legally Blonde maybe. But in life, this diversity comes to sting one back. You are so different from the typical mould, that others don't know where to fit you! And from being a model prototype, you become the outcast, the atypical! And that definitely hurts.
But take the other view. People can't cast you into any of their pre-decided moulds. They expect you to change. Change who you are, how you act, who you deal with, change everything. Project what you are in a way that appeals to others, in a way that others want to see you. That hurts all the more. Why? Because you are in a way shedding what you are, and you are turning into something you have no clue about. And in all probability, you will end up being neither yourself, nor what others want you to be, but rather a weird half-baked concoction that dangles somewhere in between. And that is certainly not very nice.
But what is wrong in being yourself? Why adhere to peer-created mores? Why be politically correct and refrain from calling a spade a spade? The answer is simple. No man is an island. You are what you are perceived to be. And you will be perceived only if others like what they perceive. I know, it is a bit circular in reasoning, but think about it. If being me is so contrary to what others perceive, then it's a sign that what I am is perhaps not as liked by others. And individuality to the extent of being loathed is definitely not what even the most individualistic, self-willed person would want.
So, till society exists, duplicity in all its forms, will perhaps persist. Perhaps that is why behavior is a science, complete with hypotheses, findings, conclusions and underlying principles.