Because they were not thinking deeply about the interview, they failed to notice when they gave a bad or rambling answer. Underprepared people often ask superficial questions that would not be asked by someone better prepared. The “C student” gets ruled out in that moment, but fails to notice because the hiring manager will almost always answer their idiotic question politely. Consequently, the “C student” often walks out of an interview thinking they nailed it. This was a good interview