New at all this

So some people in the class are much more advanced and educated in this area and may know the answer...so bare with me Im fresh out of high school and feel very intelectually inferior to the rest of you guys in the class!<--thats why i dont talk in class! So my sister works in a group home type thing and she works with, for lack of a better word, the crazies(which is her teminology) And one of her clients who stays there admitted his self there, but says there is nothing wrong with him...but he is kind of in this fantasy world where he thinks that the pop star Beyonce is harrasing him and cheated on him with the president and Jay-Z... and he calling the police on her all the time to get her away from him. He even 'brought' her in to my sisters office to have my sister talk to her to tell her to leave him alone. he even wants a restraining order! for one i dont see how you can effectivly deal with some one like that. But he says that he is fine and not crazy and he wants to go out and get a job and have a wife and kids, but he is blaming Beyonce for holding him back. What my real question is what makes people think like that? What has happened in his brain that sets off these episodes? I want to ask my sister if he has been like that his whole life. Is it possible for people to just have a severe break down that effects them for the rest of there life? What makes people go crazy? Did something go wrong in his development..or what?