If you ask me anything I don't know, I'm not going to answer.

Most people seem to be absolutely unable to say I don’t know. Impressive but true. Even if they don't know absolutely nothing about the subject, they always feel like they must give their opinion on it and say something like "I don't know anything about it, nontheless, I think that this and that!" Is it so hard to say "I can't give an opinion on it because I don't know what you're talking about."?