Ok, now, I need to B!tch about this cause it happens too often:

You make a roleplay and specifically this type of character(s) is extremely rare / killed on sight / powerful like a boss. A player comes in and wants to make that kind of character. 

Player: So yeah, I want to make this character.
GM: Alright, build up a character and make sure to leave details why / how you can play it.

Player makes a decent character. Only problem is, he does not explain why his character wasn’t killed / imprisoned / torture for life / etc. So, you go along and ask why this wouldn’t happen.

GM: So, why wasn’t it killed on sight
Player: Hummm…. “pulls out random reason”
GM: You know this and this doesn’t make sense, right?
Player: Yeah, well “pulls out other reason”
GM: Ok, well, if you change this this and this than it should work.
Player: But it ruins the character
GM: Yes but logically, it is the one of the many ways you can choose.
Player: But I prefer this way…
GM: But that won’t work

It can end in one of three ways:

1. The player accepts the changes and does his best to adapt and make it work
2. The player wants to keep the same character and the DM
2.1 says change it or it is denied
2.2 says alright and goes with it (Very rare)
3. The player just leaves, not satisfied.

Reason 2 and 3…