Here are some examples where Anne Frank thinks that Peter has inferiority complex:
Peter has a terrible inferiority complex. For instance, he always thinks that he is so stupid, and we are so clever.
He told me he wanted to go to the Dutch East Indies and live on a plantation later on. He talked about his home life, about the black market, and then he said that he felt so useless.
He talked about the Jews. He would have found it much easier if he’d been a Christian and if he could be one after the war.
Anne Frank's Diary is not a novel or a tale of the imagination. It is the diary kept by a young Jewish girl for the two years she was forced to remain in hiding by the Nazi persecution of the Jews of Europe. Between June 1942 and August 1944, from Anne's thirteenth birthday until shortly after her fifteenth birthday, Anne Frank recorded her feelings, her emotions, and her thoughts, as well as the events that happened to her, in the diary which her father had given her as a birthday present.
Check out 10 Things to Know About Anne Frank's The Diary of a Young Girl at MentalFloss.