I think we have found a winner. By unanimous agreement, the answer is YES!

Kidding aside, it's interesting to learn that every single person who has responded believes unequivocally that we can say things that are lies and believe they are true.

I can think of two instances -- when a person is in denial and doesn't see reality clearly, as a previous writer noted. Sociopaths have a hard time distinguishing truth from lies, too. I'm sure there are other categories. I'm pretty sure that there have been times in my life when I might be unwittingly guilty of this.