Both, I guess. The environment you grew up in and your experiences shaped your way of thinking and feeling. It's like thinking about that one guy who teased you when you were a kid and made you feel this or that way, and then you just assume everyone's like that and everyone's judging you negatively wherever you go. If you look at it rationally, and slowly realize that's not even close to being true, you can challenge those thought patterns and replace them with new ways of thinking and acting.
Makes sense, so the best way to breakdown core beliefs is self talk? or CBT?