"Most people I know failed at certain subjects in school (maybe not by getting Fs, but by struggling with those subjects for years), and now have simply decided "I’m not a ______ person" or "I just don’t get _______", e.g. "I’m not a Math person" or "I just don’t get Shakespeare." That absolves them from trying. Which keeps them from failing. Which keeps them from learning."
Quote from Marcus Geduld’s answer on Quora, on "Why do we get frustrated when learning something"